diff --git a/src/api/mavedb/index.ts b/src/api/mavedb/index.ts
index c097c748..3a92e5cf 100644
--- a/src/api/mavedb/index.ts
+++ b/src/api/mavedb/index.ts
@@ -1,18 +1,3 @@
-import {isAxiosError} from 'axios'
-
-export interface ErrorResponse {
-  status: number
-  data?: Record<string, unknown>
-}
-
-/** Extract a normalized response from a caught Axios error. */
-export function getErrorResponse(e: unknown): ErrorResponse {
-  if (isAxiosError(e) && e.response) {
-    return {status: e.response.status, data: e.response.data as Record<string, unknown>}
-  }
-  return {status: 500}
-}
-
 export * from './access-keys'
 export * from './calibrations'
 export * from './collections'
diff --git a/src/api/mavedb/score-sets.ts b/src/api/mavedb/score-sets.ts
index f2211a84..24ef5517 100644
--- a/src/api/mavedb/score-sets.ts
+++ b/src/api/mavedb/score-sets.ts
@@ -7,13 +7,10 @@ type ScoreSetSearch = components['schemas']['ScoreSetsSearch']
 type ScoreSetsSearchResponse = components['schemas']['ScoreSetsSearchResponse']
 export type ScoreSetsSearchFilterOptionsResponse = components['schemas']['ScoreSetsSearchFilterOptionsResponse']
 
-const HISTOGRAM_VARIANT_DATA_NAMESPACES = ['vep', 'scores', 'clingen']
+const HISTOGRAM_VARIANT_DATA_NAMESPACES = ['vep', 'scores', 'clingen', 'mavedb']
 
-function scoreSetVariantDataParams(
-  options: {includePostMappedHgvs?: boolean; namespaces?: string[]} = {}
-): URLSearchParams {
+function scoreSetVariantDataParams(options: {namespaces?: string[]} = {}): URLSearchParams {
   const params = new URLSearchParams()
-  if (options.includePostMappedHgvs) params.append('include_post_mapped_hgvs', 'true')
   for (const namespace of options.namespaces ?? []) params.append('namespaces', namespace)
   return params
 }
@@ -25,10 +22,7 @@ function scoreSetVariantDataUrl(urn: string, params: URLSearchParams = new URLSe
 }
 
 export function histogramScoreSetVariantDataUrl(urn: string): string {
-  return scoreSetVariantDataUrl(
-    urn,
-    scoreSetVariantDataParams({includePostMappedHgvs: true, namespaces: HISTOGRAM_VARIANT_DATA_NAMESPACES})
-  )
+  return scoreSetVariantDataUrl(urn, scoreSetVariantDataParams({namespaces: HISTOGRAM_VARIANT_DATA_NAMESPACES}))
 }
 
 // ---------------------------------------------------------------------------
@@ -103,17 +97,32 @@ export async function publishScoreSet(urn: string) {
 }
 
 export async function getScoreSetClinicalControlOptions(urn: string) {
-  const response = await axios.get(`${config.apiBaseUrl}/score-sets/${encodeURIComponent(urn)}/clinical-controls/options`)
+  const response = await axios.get(
+    `${config.apiBaseUrl}/score-sets/${encodeURIComponent(urn)}/clinical-controls/options`
+  )
   return response.data
 }
 
 export async function downloadScoreSetFile(urn: string, type: 'scores' | 'counts'): Promise<string> {
   const response = await axios.get(
-    `${config.apiBaseUrl}/score-sets/${encodeURIComponent(urn)}/${type}?drop_na_columns=true`
+    `${config.apiBaseUrl}/score-sets/${encodeURIComponent(urn)}/${type}?drop_unused_hgvs_columns=true`
   )
   return response.data
 }
 
+/**
+ * Fetch the CSV column namespaces this score set has data for.
+ */
+export async function getScoreSetCsvNamespaces(
+  urn: string,
+  signal?: AbortSignal
+): Promise<components['schemas']['AvailableCsvNamespace'][]> {
+  const response = await axios.get(`${config.apiBaseUrl}/score-sets/${encodeURIComponent(urn)}/csv-namespaces`, {
+    signal
+  })
+  return response.data
+}
+
 export async function downloadScoreSetVariantData(urn: string, params: URLSearchParams): Promise<string> {
   const response = await axios.get(scoreSetVariantDataUrl(urn, params))
   return response.data
@@ -121,14 +130,14 @@ export async function downloadScoreSetVariantData(urn: string, params: URLSearch
 
 export async function getScoreSetScoresPreview(urn: string): Promise<string> {
   const response = await axios.get(
-    `${config.apiBaseUrl}/score-sets/${encodeURIComponent(urn)}/scores?drop_na_columns=true`
+    `${config.apiBaseUrl}/score-sets/${encodeURIComponent(urn)}/scores?drop_unused_hgvs_columns=true`
   )
   return response.data
 }
 
 export async function getScoreSetCountsPreview(urn: string): Promise<string> {
   const response = await axios.get(
-    `${config.apiBaseUrl}/score-sets/${encodeURIComponent(urn)}/counts?drop_na_columns=true`
+    `${config.apiBaseUrl}/score-sets/${encodeURIComponent(urn)}/counts?drop_unused_hgvs_columns=true`
   )
   return response.data
 }
@@ -138,7 +147,9 @@ export async function downloadMappedVariants(urn: string) {
   return response.data
 }
 
-export async function getRecentlyPublishedScoreSets(signal?: AbortSignal): Promise<components['schemas']['ScoreSet'][]> {
+export async function getRecentlyPublishedScoreSets(
+  signal?: AbortSignal
+): Promise<components['schemas']['ScoreSet'][]> {
   const response = await axios.get(`${config.apiBaseUrl}/score-sets/recently-published`, {
     headers: {accept: 'application/json'},
     signal
diff --git a/src/api/mavedb/variants.ts b/src/api/mavedb/variants.ts
index f0db95a4..24f5a31c 100644
--- a/src/api/mavedb/variants.ts
+++ b/src/api/mavedb/variants.ts
@@ -8,6 +8,7 @@ type ScoreSet = components['schemas']['ScoreSet']
 type VariantEffectMeasurementWithScoreSet = components['schemas']['VariantEffectMeasurementWithScoreSet']
 type ClingenAlleleIdVariantLookupResponse = components['schemas']['ClingenAlleleIdVariantLookupResponse']
 type MappedVariant = components['schemas']['MappedVariant']
+type AvailableCsvNamespace = components['schemas']['AvailableCsvNamespace']
 
 export async function lookupVariantsByClingenId(
   clingenAlleleIds: string[]
@@ -47,3 +48,24 @@ export async function getScoreSet(urn: string): Promise<ScoreSet> {
   const response = await axios.get(`${config.apiBaseUrl}/score-sets/${encodeURIComponent(urn)}`)
   return response.data
 }
+
+/**
+ * Fetch the CSV column namespaces this variant has data for.
+ */
+export async function getVariantCsvNamespaces(urn: string, signal?: AbortSignal): Promise<AvailableCsvNamespace[]> {
+  const response = await axios.get(`${config.apiBaseUrl}/variants/${encodeURIComponent(urn)}/csv-namespaces`, {signal})
+  return response.data
+}
+
+export function variantCsvUrl(urn: string, namespaces?: string[]): string {
+  const params = new URLSearchParams()
+  for (const namespace of namespaces ?? []) params.append('namespaces', namespace)
+  const query = params.toString()
+  const baseUrl = `${config.apiBaseUrl}/variants/${encodeURIComponent(urn)}/csv`
+  return query ? `${baseUrl}?${query}` : baseUrl
+}
+
+export async function downloadVariantCsv(urn: string, namespaces?: string[]): Promise<string> {
+  const response = await axios.get(variantCsvUrl(urn, namespaces))
+  return response.data
+}
diff --git a/src/components/collection/CollectionDataSetEditor.vue b/src/components/collection/CollectionDataSetEditor.vue
index 5e962885..9a4c997f 100644
--- a/src/components/collection/CollectionDataSetEditor.vue
+++ b/src/components/collection/CollectionDataSetEditor.vue
@@ -101,7 +101,7 @@ import useItem from '@/composition/item.ts'
 import {addCollectionScoreSet, addCollectionExperiment} from '@/api/mavedb/collections'
 import {getScoreSet} from '@/api/mavedb/variants'
 import {getExperiment} from '@/api/mavedb/experiments'
-import {getErrorResponse} from '@/api/mavedb'
+import {getErrorResponse} from '@/lib/errors'
 import {type DataSetType, DATA_SET_TYPE_LABELS} from '@/lib/collections'
 import MvEmailPrompt from '@/components/common/MvEmailPrompt.vue'
 import {components} from '@/schema/openapi'
diff --git a/src/components/common/MvCsvColumnDialog.vue b/src/components/common/MvCsvColumnDialog.vue
new file mode 100644
index 00000000..afc2e983
--- /dev/null
+++ b/src/components/common/MvCsvColumnDialog.vue
@@ -0,0 +1,129 @@
+<template>
+  <PDialog
+    :base-z-index="901"
+    :header="header"
+    modal
+    :style="{width: '30rem'}"
+    :visible="visible"
+    @show="load()"
+    @update:visible="$emit('update:visible', $event)">
+    <MvLoader v-if="loading" />
+    <MvErrorState
+      v-else-if="error"
+      description="The list of available columns could not be loaded."
+      title="Could not load download options"
+      @retry="load()" />
+    <div v-else class="flex flex-col gap-4 py-2">
+      <div class="flex items-center justify-between border-b border-border-light pb-2">
+        <span class="text-sm text-text-muted">{{ selectionSummary }}</span>
+        <button
+          class="cursor-pointer border-none bg-transparent text-xs-plus font-semibold text-sage hover:underline"
+          type="button"
+          @click="toggleAll()">
+          {{ allSelected ? 'Select none' : 'Select all' }}
+        </button>
+      </div>
+
+      <div v-for="section in sections" :key="section.group" class="flex flex-col gap-2">
+        <span class="text-xs font-bold uppercase tracking-wide text-text-muted">{{ section.title }}</span>
+        <template v-for="subsection in section.subsections" :key="subsection.label ?? '_'">
+          <!-- Only present when the section spans more than one score set, e.g. a variant measured in
+               several assays, each with its own calibrations. -->
+          <span v-if="subsection.label" class="text-xs text-text-muted" :title="subsection.urn ?? undefined">{{
+            subsection.label
+          }}</span>
+          <label
+            v-for="entry in subsection.namespaces"
+            :key="entry.namespace"
+            class="flex cursor-pointer items-center gap-2 text-sm"
+            :class="{'pl-3': subsection.label}">
+            <Checkbox v-model="selected" :value="entry.namespace" />
+            {{ entry.label }}
+          </label>
+        </template>
+      </div>
+
+      <div v-if="formattingExtraOptions.length > 0" class="flex flex-col gap-2 border-t border-border-light pt-3">
+        <span class="text-xs font-bold uppercase tracking-wide text-text-muted">Options</span>
+        <label
+          v-for="option in formattingExtraOptions"
+          :key="option.value"
+          class="flex cursor-pointer items-center gap-2 text-sm">
+          <Checkbox v-model="selectedExtras" :value="option.value" />
+          {{ option.label }}
+        </label>
+      </div>
+    </div>
+
+    <template #footer>
+      <PButton label="Cancel" severity="secondary" size="small" @click="$emit('update:visible', false)" />
+      <PButton
+        :disabled="loading || !!error || selectedColumnGroups === 0"
+        icon="pi pi-download"
+        label="Download"
+        size="small"
+        @click="confirm" />
+    </template>
+  </PDialog>
+</template>
+
+<script lang="ts">
+import Button from 'primevue/button'
+import Checkbox from 'primevue/checkbox'
+import PDialog from 'primevue/dialog'
+import {computed, defineComponent, type PropType} from 'vue'
+
+import MvErrorState from '@/components/common/MvErrorState.vue'
+import MvLoader from '@/components/common/MvLoader.vue'
+import {useCsvNamespaces, type CsvExtraOption} from '@/composables/use-csv-namespaces'
+
+/**
+ * Column picker for the CSV exports, shared by the score set and variant pages.
+ *
+ * Namespace checkboxes come from the API, so neither page maintains its own list or labels. Non-namespace
+ * query flags are passed in as `extraOptions` and returned separately as `extras`.
+ *
+ * Download stays disabled until a namespace is checked, so the emitted selection always names its
+ * columns — there is no "empty means all" rule for callers to know.
+ */
+export default defineComponent({
+  name: 'MvCsvColumnDialog',
+
+  components: {Checkbox, MvErrorState, MvLoader, PButton: Button, PDialog},
+
+  props: {
+    visible: {type: Boolean, required: true},
+    /** The score set or variant whose columns to offer. */
+    urn: {type: String as PropType<string | null>, default: null},
+    kind: {type: String as PropType<'scoreSet' | 'variant'>, required: true},
+    header: {type: String, default: 'Choose columns'},
+    /** Formatting flags, e.g. omitting unused HGVS columns. Returned as `extras` on confirm. */
+    extraOptions: {type: Array as PropType<CsvExtraOption[]>, default: () => []}
+  },
+
+  emits: ['update:visible', 'confirm'],
+
+  setup(props) {
+    // The whole selection model lives in the composable, where it is unit-testable without a DOM —
+    // including the extras, so the count and "Select all" cover every checkbox on screen. Spread so the
+    // template reads the refs directly rather than reaching through a wrapper object.
+    return {
+      ...useCsvNamespaces({
+        urn: computed(() => props.urn),
+        kind: props.kind,
+        extraOptions: computed(() => props.extraOptions)
+      })
+    }
+  },
+
+  methods: {
+    confirm() {
+      this.$emit('confirm', {
+        namespaces: [...this.selected],
+        extras: [...this.selectedExtras]
+      })
+      this.$emit('update:visible', false)
+    }
+  }
+})
+</script>
diff --git a/src/components/common/MvVariantPreview.vue b/src/components/common/MvVariantPreview.vue
index 85fd7762..e0d2c4b0 100644
--- a/src/components/common/MvVariantPreview.vue
+++ b/src/components/common/MvVariantPreview.vue
@@ -10,28 +10,32 @@
       <div class="flex flex-wrap items-center gap-2">
         <PButton
           v-if="!processingErrors"
+          :disabled="fileDownloadInProgress"
           icon="pi pi-download"
           label="Scores"
           severity="secondary"
           size="small"
-          @click="downloadFile('scores')"
-        />
+          @click="downloadFile('scores')" />
         <PButton
           v-if="!processingErrors && hasCountData"
+          :disabled="fileDownloadInProgress"
           icon="pi pi-download"
           label="Counts"
           severity="secondary"
           size="small"
-          @click="downloadFile('counts')"
-        />
+          @click="downloadFile('counts')" />
         <PButton
           v-if="!processingErrors"
+          :disabled="fileDownloadInProgress"
           icon="pi pi-sliders-h"
           label="Custom Data"
           severity="secondary"
           size="small"
-          @click="customDialogVisible = true"
-        />
+          @click="customDialogVisible = true" />
+        <span v-if="fileDownloadInProgress" aria-live="polite" class="flex items-center gap-2 text-xs text-text-muted">
+          <i class="pi pi-spin pi-spinner text-xs" />
+          Preparing {{ fileDownloadLabel }}…
+        </span>
         <slot name="actions" />
       </div>
     </div>
@@ -82,8 +86,7 @@
       </div>
       <div v-else-if="countsRows.length > 0">
         <div
-          class="flex items-center justify-between border-b border-border-light border-t bg-bg px-4 py-2 tablet:px-5"
-        >
+          class="flex items-center justify-between border-b border-border-light border-t bg-bg px-4 py-2 tablet:px-5">
           <span class="text-xs font-semibold uppercase tracking-wider text-text-muted">Counts</span>
           <span class="text-xs text-text-muted">
             Showing {{ countsRows.length }} of {{ countsData.length.toLocaleString() }}
@@ -109,34 +112,26 @@
 
       <div
         v-if="scoresRows.length === 0 && countsRows.length === 0"
-        class="px-5 py-8 text-center text-sm italic text-text-muted"
-      >
+        class="px-5 py-8 text-center text-sm italic text-text-muted">
         No data available.
       </div>
     </template>
   </div>
 
-  <!-- Custom data dialog -->
-  <PDialog v-model:visible="customDialogVisible" header="Custom Data Download" modal :style="{width: '28rem'}">
-    <div class="flex flex-col gap-3 py-2">
-      <label v-for="opt in dataTypeOptions" :key="opt.value" class="flex cursor-pointer items-center gap-2 text-sm">
-        <Checkbox v-model="selectedDataOptions" :value="opt.value" />
-        {{ opt.label }}
-      </label>
-    </div>
-    <template #footer>
-      <PButton label="Cancel" severity="secondary" size="small" @click="customDialogVisible = false" />
-      <PButton icon="pi pi-download" label="Download" size="small" @click="downloadMultipleData" />
-    </template>
-  </PDialog>
+  <MvCsvColumnDialog
+    v-model:visible="customDialogVisible"
+    :extra-options="extraDownloadOptions"
+    header="Custom data download"
+    kind="scoreSet"
+    :urn="scoreSet.urn"
+    @confirm="downloadMultipleData" />
 </template>
 
 <script lang="ts">
 import {defineComponent, toRef, type PropType} from 'vue'
 import PButton from 'primevue/button'
-import Checkbox from 'primevue/checkbox'
-import PDialog from 'primevue/dialog'
 
+import MvCsvColumnDialog from '@/components/common/MvCsvColumnDialog.vue'
 import {getScoreSetScoresPreview, getScoreSetCountsPreview} from '@/api/mavedb'
 import MvStatusMessage from '@/components/common/MvStatusMessage.vue'
 import MvLoader from '@/components/common/MvLoader.vue'
@@ -151,7 +146,7 @@ const MAX_ROWS = 5
 export default defineComponent({
   name: 'MvVariantPreview',
 
-  components: {Checkbox, MvLoader, MvStatusMessage, PButton, PDialog},
+  components: {MvCsvColumnDialog, MvLoader, MvStatusMessage, PButton},
 
   props: {
     scoreSet: {type: Object as PropType<ScoreSet>, required: true}
@@ -192,18 +187,6 @@ export default defineComponent({
     },
     countsRows(): ScoresOrCountsRow[] {
       return this.hasCountData ? this.countsData.slice(0, MAX_ROWS) : []
-    },
-    dataTypeOptions(): Array<{label: string; value: string}> {
-      const options = [
-        {label: 'Scores', value: 'scores'},
-        {label: 'Mapped HGVS', value: 'mappedHgvs'},
-        {label: 'Custom columns', value: 'includeCustomColumns'},
-        {label: 'Without NA columns', value: 'dropNaColumns'}
-      ]
-      if (this.hasCountData) {
-        options.splice(1, 0, {label: 'Counts', value: 'counts'})
-      }
-      return options
     }
   },
 
diff --git a/src/components/score-set/ScoreSetDownloads.vue b/src/components/score-set/ScoreSetDownloads.vue
index 79b98bf9..612c827f 100644
--- a/src/components/score-set/ScoreSetDownloads.vue
+++ b/src/components/score-set/ScoreSetDownloads.vue
@@ -2,14 +2,22 @@
   <div class="rounded-lg border border-border bg-white p-5">
     <h3 class="mave-section-title">Download files</h3>
     <div class="flex flex-wrap gap-2">
-      <PButton icon="pi pi-download" label="Scores" severity="secondary" size="small" @click="downloadFile('scores')" />
+      <PButton
+        :disabled="fileDownloadInProgress"
+        icon="pi pi-download"
+        label="Scores"
+        severity="secondary"
+        size="small"
+        @click="reportingFailure('scores', () => downloadFile('scores'))"
+      />
       <PButton
         v-if="hasCounts"
+        :disabled="fileDownloadInProgress"
         icon="pi pi-download"
         label="Counts"
         severity="secondary"
         size="small"
-        @click="downloadFile('counts')"
+        @click="reportingFailure('counts', () => downloadFile('counts'))"
       />
       <PButton
         v-if="!isMetaDataEmpty"
@@ -20,41 +28,53 @@
         @click="downloadMetadata"
       />
       <PButton
+        :disabled="fileDownloadInProgress"
         icon="pi pi-download"
         label="Mapped Variants"
         severity="secondary"
         size="small"
-        @click="downloadMappedVariantsFile"
+        @click="reportingFailure('mapped variants', downloadMappedVariantsFile)"
       />
 
-      <div class="relative inline-block">
-        <SplitButton
-          :button-props="{class: 'p-button-sm p-button-secondary'}"
-          :disabled="annotatedDownloadInProgress"
-          label="Annotated Variants"
-          :menu-button-props="{class: 'p-button-sm p-button-secondary'}"
-          :model="annotatedVariantDownloadOptions"
-          @click="
-            annotatedVariantDownloadOptions[0]?.command?.({
-              originalEvent: $event,
-              item: annotatedVariantDownloadOptions[0]
-            })
-          "
-        />
-        <div v-if="annotatedDownloadInProgress" class="absolute inset-x-0 top-full mt-1">
-          <ProgressBar show-value style="height: 1.5em" :value="annotatedDownloadProgress" />
-        </div>
-      </div>
+      <SplitButton
+        :button-props="{class: 'p-button-sm p-button-secondary'}"
+        :disabled="fileDownloadInProgress"
+        label="Annotated Variants"
+        :menu-button-props="{class: 'p-button-sm p-button-secondary'}"
+        :model="annotatedVariantDownloadOptions"
+        @click="
+          annotatedVariantDownloadOptions[0]?.command?.({
+            originalEvent: $event,
+            item: annotatedVariantDownloadOptions[0]
+          })
+        "
+      />
 
       <PButton
+        :disabled="fileDownloadInProgress"
         icon="pi pi-sliders-h"
-        label="Custom Data"
+        label="Custom CSV"
         severity="secondary"
         size="small"
         @click="customDialogVisible = true"
       />
     </div>
 
+    <!-- One bar for every download on this panel. Determinate only for the VA-Spec streams, which can
+         count records; see `fileDownloadProgress` in use-score-set-downloads. -->
+    <div v-if="fileDownloadInProgress" aria-live="polite" class="mt-3 flex items-center gap-2">
+      <ProgressBar
+        class="grow"
+        :mode="fileDownloadProgress === null ? 'indeterminate' : 'determinate'"
+        style="height: 1.2em"
+        :value="fileDownloadProgress ?? 0"
+      />
+      <span class="whitespace-nowrap text-xs text-text-muted">
+        Preparing {{ fileDownloadLabel }}…
+        <template v-if="fileDownloadProgress !== null">{{ fileDownloadProgress }}%</template>
+      </span>
+    </div>
+
     <!-- Galaxy integration -->
     <div v-if="requestFromGalaxy === '1'" class="mt-3 border-t border-border-light pt-3">
       Send files to <a :href="galaxyUrl">Galaxy</a>
@@ -65,37 +85,25 @@
       </div>
     </div>
 
-    <!-- Custom data dialog -->
-    <PDialog
+    <MvCsvColumnDialog
       v-model:visible="customDialogVisible"
-      :base-z-index="901"
-      header="Custom Data Download"
-      modal
-      :style="{width: '28rem'}"
-    >
-      <div class="flex flex-col gap-3 py-2">
-        <label v-for="opt in dataTypeOptions" :key="opt.value" class="flex cursor-pointer items-center gap-2 text-sm">
-          <Checkbox v-model="selectedDataOptions" :value="opt.value" />
-          {{ opt.label }}
-        </label>
-      </div>
-      <template #footer>
-        <PButton label="Cancel" severity="secondary" size="small" @click="customDialogVisible = false" />
-        <PButton icon="pi pi-download" label="Download" size="small" @click="handleCustomDownload" />
-      </template>
-    </PDialog>
+      :extra-options="extraDownloadOptions"
+      header="Custom data download"
+      kind="scoreSet"
+      :urn="scoreSet.urn"
+      @confirm="handleCustomDownload"
+    />
   </div>
 </template>
 
 <script lang="ts">
 import {defineComponent, toRef, type PropType} from 'vue'
 import PButton from 'primevue/button'
-import Checkbox from 'primevue/checkbox'
-import PDialog from 'primevue/dialog'
 import type {MenuItem} from 'primevue/menuitem'
 import ProgressBar from 'primevue/progressbar'
 import SplitButton from 'primevue/splitbutton'
 
+import MvCsvColumnDialog from '@/components/common/MvCsvColumnDialog.vue'
 import {useScoreSetDownloads} from '@/composables/use-score-set-downloads'
 import config from '@/config'
 import type {components} from '@/schema/openapi'
@@ -106,7 +114,7 @@ type ScoreSet = components['schemas']['ScoreSet']
 export default defineComponent({
   name: 'ScoreSetDownloads',
 
-  components: {PButton, Checkbox, PDialog, ProgressBar, SplitButton},
+  components: {MvCsvColumnDialog, PButton, ProgressBar, SplitButton},
 
   props: {
     hasCounts: {type: Boolean, default: false},
@@ -117,9 +125,7 @@ export default defineComponent({
   },
 
   setup(props) {
-    const scoreSetRef = toRef(props, 'scoreSet')
-    const hasCountsRef = toRef(props, 'hasCounts')
-    const downloads = useScoreSetDownloads({scoreSet: scoreSetRef, hasCounts: hasCountsRef})
+    const downloads = useScoreSetDownloads({scoreSet: toRef(props, 'scoreSet')})
 
     const routeProps = store.state.routeProps as {galaxyUrl: string; toolId: string; requestFromGalaxy: string}
 
@@ -138,19 +144,28 @@ export default defineComponent({
       if (this.hasPathogenicityCalibrations) {
         options.push({
           label: 'Pathogenicity Statement',
-          command: () => this.streamVariantAnnotations('pathogenicity-statement')
+          command: () =>
+            this.reportingFailure('Pathogenicity Statement', () =>
+              this.streamVariantAnnotations('pathogenicity-statement', 'Pathogenicity Statement')
+            )
         })
       }
       if (this.hasFunctionalImpactCalibrations) {
         options.push({
           label: 'Functional Impact Statement',
-          command: () => this.streamVariantAnnotations('functional-statement')
+          command: () =>
+            this.reportingFailure('Functional Impact Statement', () =>
+              this.streamVariantAnnotations('functional-statement', 'Functional Impact Statement')
+            )
         })
       }
 
       options.push({
         label: 'Functional Study Result',
-        command: () => this.streamVariantAnnotations('study-result')
+        command: () =>
+          this.reportingFailure('Functional Study Result', () =>
+            this.streamVariantAnnotations('study-result', 'Functional Study Result')
+          )
       })
 
       return options
@@ -162,14 +177,29 @@ export default defineComponent({
   },
 
   methods: {
-    async handleCustomDownload() {
+    /**
+     * Run a download, reporting any failure as a toast.
+     *
+     * Without this a rejection from a template `@click` is an unhandled promise, which is how a truncated
+     * or out-of-memory annotation download used to surface: a console error and nothing in the UI.
+     */
+    async reportingFailure(what: string, download: () => Promise<unknown>) {
       try {
-        await this.downloadMultipleData()
-      } catch {
-        this.$toast.add({severity: 'error', summary: 'Error downloading custom data', life: 3000})
+        await download()
+      } catch (error: unknown) {
+        this.$toast.add({
+          severity: 'error',
+          summary: `Could not download ${what}`,
+          detail: error instanceof Error ? error.message : undefined,
+          life: 6000
+        })
       }
     },
 
+    async handleCustomDownload(selection: {namespaces: string[]; extras: string[]}) {
+      await this.reportingFailure('custom data', () => this.downloadMultipleData(selection))
+    },
+
     async sendToGalaxy(downloadType: string) {
       try {
         const baseApiUrl = `${config.apiBaseUrl}/score-sets/${this.scoreSet.urn}`
@@ -205,3 +235,15 @@ export default defineComponent({
   }
 })
 </script>
+
+<style scoped>
+/*
+ * PrimeVue animates the determinate fill with `transition: width 1s ease-in-out` from 0%. A download that
+ * finishes quickly reaches 100% and unmounts the bar before the animation lands, leaving a fifth-full bar
+ * beside a label reading 100% — and each new value restarts the animation, so the fill lags throughout.
+ * Progress arrives in jumps of a whole chunk anyway, so track the value exactly rather than easing to it.
+ */
+:deep(.p-progressbar-determinate .p-progressbar-value) {
+  transition: none;
+}
+</style>
diff --git a/src/components/screens/CollectionView.vue b/src/components/screens/CollectionView.vue
index e5f9afa7..78bfd8fa 100644
--- a/src/components/screens/CollectionView.vue
+++ b/src/components/screens/CollectionView.vue
@@ -258,7 +258,7 @@ import {deleteCollection, removeCollectionEntity, updateCollection} from '@/api/
 import {useDatasetPermissions} from '@/composables/use-dataset-permissions'
 import type {RowAction} from '@/components/common/MvRowActionMenu.vue'
 import {components} from '@/schema/openapi'
-import {getErrorResponse} from '@/api/mavedb'
+import {getErrorResponse} from '@/lib/errors'
 
 type Collection = components['schemas']['Collection']
 type User = components['schemas']['User']
diff --git a/src/components/screens/ExperimentCreator.vue b/src/components/screens/ExperimentCreator.vue
index 4d11926d..407d70a0 100644
--- a/src/components/screens/ExperimentCreator.vue
+++ b/src/components/screens/ExperimentCreator.vue
@@ -172,7 +172,8 @@ import useScopedId from '@/composables/scoped-id'
 import {useExperimentKeywords} from '@/composables/use-experiment-keywords'
 import {useJsonFileField} from '@/composables/use-json-file-field'
 import {usePublicationIdentifiers} from '@/composables/use-publication-identifiers'
-import {createExperiment, getErrorResponse} from '@/api/mavedb'
+import {createExperiment} from '@/api/mavedb'
+import {getErrorResponse} from '@/lib/errors'
 import useAuth from '@/composition/auth'
 import {useKeywordOptions} from '@/composables/use-keyword-options'
 import {normalizeDoiArray, normalizeRawReadArray, normalizeContributorArray} from '@/lib/form-helpers'
diff --git a/src/components/screens/ExperimentEditor.vue b/src/components/screens/ExperimentEditor.vue
index 590165a9..940cb461 100644
--- a/src/components/screens/ExperimentEditor.vue
+++ b/src/components/screens/ExperimentEditor.vue
@@ -111,7 +111,8 @@ import {useExperimentKeywords} from '@/composables/use-experiment-keywords'
 import {useJsonFileField} from '@/composables/use-json-file-field'
 import {usePublicationIdentifiers, type PublicationIdentifier} from '@/composables/use-publication-identifiers'
 import useAuth from '@/composition/auth'
-import {updateExperiment, getErrorResponse} from '@/api/mavedb'
+import {updateExperiment} from '@/api/mavedb'
+import {getErrorResponse} from '@/lib/errors'
 import useItem from '@/composition/item.ts'
 import {useKeywordOptions} from '@/composables/use-keyword-options'
 import {normalizeDoiArray, normalizeRawReadArray, normalizeContributorArray} from '@/lib/form-helpers'
diff --git a/src/components/screens/ScoreSetCalibrationsView.vue b/src/components/screens/ScoreSetCalibrationsView.vue
index 983695a3..373c2be7 100644
--- a/src/components/screens/ScoreSetCalibrationsView.vue
+++ b/src/components/screens/ScoreSetCalibrationsView.vue
@@ -232,7 +232,6 @@ import {
   getScoreSetCalibrations
 } from '@/api/mavedb'
 import {useDatasetPermissions} from '@/composables/use-dataset-permissions'
-import axios from 'axios'
 import Button from 'primevue/button'
 import Column from 'primevue/column'
 import DataTable from 'primevue/datatable'
@@ -242,6 +241,7 @@ import useAuth from '@/composition/auth'
 import {useCalibrationDialog} from '@/composables/use-calibration-dialog'
 import MvPageLoading from '@/components/common/MvPageLoading.vue'
 import CalibrationTable from '@/components/calibration/CalibrationTable.vue'
+import {describeRequestError} from '@/lib/errors'
 import {getScoreSetShortName} from '@/lib/score-sets'
 import {useConfirm} from 'primevue/useconfirm'
 import CalibrationEditor from '@/components/calibration/CalibrationEditor.vue'
@@ -258,17 +258,6 @@ type ScoreSet = components['schemas']['ScoreSet']
 const CALIBRATION_ACTIONS = ['update', 'delete', 'publish', 'change_rank'] as const
 type CalibrationAuthorizations = Record<(typeof CALIBRATION_ACTIONS)[number], boolean>
 
-function extractErrorDetail(error: unknown): string {
-  if (
-    axios.isAxiosError(error) &&
-    error.response?.data?.detail &&
-    (typeof error.response.data.detail === 'string' || error.response.data.detail instanceof String)
-  ) {
-    return error.response.data.detail as string
-  }
-  return String(error)
-}
-
 export default {
   name: 'ScoreSetCalibrationsView',
   components: {
@@ -510,7 +499,7 @@ export default {
             this.$toast.add({
               severity: 'error',
               summary: 'Calibration Not Published',
-              detail: `An error occurred while publishing the calibration: ${extractErrorDetail(error)}. Please try again later.`,
+              detail: `An error occurred while publishing the calibration: ${describeRequestError(error)}. Please try again later.`,
               life: 4000
             })
           }
@@ -534,7 +523,7 @@ export default {
         this.$toast.add({
           severity: 'error',
           summary: 'Calibration Not Demoted',
-          detail: `An error occurred while demoting the calibration: ${extractErrorDetail(error)}. Please try again later.`,
+          detail: `An error occurred while demoting the calibration: ${describeRequestError(error)}. Please try again later.`,
           life: 4000
         })
       }
@@ -555,7 +544,7 @@ export default {
         this.$toast.add({
           severity: 'error',
           summary: 'Calibration Not Promoted',
-          detail: `An error occurred while promoting the calibration: ${extractErrorDetail(error)}. Please try again later.`,
+          detail: `An error occurred while promoting the calibration: ${describeRequestError(error)}. Please try again later.`,
           life: 4000
         })
       }
@@ -583,7 +572,7 @@ export default {
             this.$toast.add({
               severity: 'error',
               summary: 'Calibration Not Deleted',
-              detail: `An error occurred while deleting the calibration: ${extractErrorDetail(error)}. Please try again later.`,
+              detail: `An error occurred while deleting the calibration: ${describeRequestError(error)}. Please try again later.`,
               life: 4000
             })
           }
@@ -610,7 +599,7 @@ export default {
         this.$toast.add({
           severity: 'error',
           summary: 'Download Failed',
-          detail: `An error occurred while downloading the calibrations: ${extractErrorDetail(error)}. Please try again later.`,
+          detail: `An error occurred while downloading the calibrations: ${describeRequestError(error)}. Please try again later.`,
           life: 4000
         })
       }
diff --git a/src/components/screens/ScoreSetCreator.vue b/src/components/screens/ScoreSetCreator.vue
index 9d65a6cc..7a87d88e 100644
--- a/src/components/screens/ScoreSetCreator.vue
+++ b/src/components/screens/ScoreSetCreator.vue
@@ -405,7 +405,8 @@ import ToggleSwitch from 'primevue/toggleswitch'
 import {ref} from 'vue'
 import {useHead} from '@unhead/vue'
 
-import {getExperiment, searchMyExperiments, createScoreSet, uploadVariantData, getErrorResponse} from '@/api/mavedb'
+import {getExperiment, searchMyExperiments, createScoreSet, uploadVariantData} from '@/api/mavedb'
+import {getErrorResponse} from '@/lib/errors'
 import CalibrationEditor from '@/components/calibration/CalibrationEditor.vue'
 import MvEmailPrompt from '@/components/common/MvEmailPrompt.vue'
 import ScoreSetContextFields from '@/components/forms/ScoreSetContextFields.vue'
diff --git a/src/components/screens/ScoreSetEditor.vue b/src/components/screens/ScoreSetEditor.vue
index 02762aee..49fbf953 100644
--- a/src/components/screens/ScoreSetEditor.vue
+++ b/src/components/screens/ScoreSetEditor.vue
@@ -257,7 +257,8 @@ import {useHead} from '@unhead/vue'
 
 import ToggleSwitch from 'primevue/toggleswitch'
 
-import {searchMyExperiments, updateScoreSetWithVariants, getErrorResponse} from '@/api/mavedb'
+import {searchMyExperiments, updateScoreSetWithVariants} from '@/api/mavedb'
+import {getErrorResponse} from '@/lib/errors'
 import MvEmailPrompt from '@/components/common/MvEmailPrompt.vue'
 import MvEmptyState from '@/components/common/MvEmptyState.vue'
 import ScoreSetContextFields from '@/components/forms/ScoreSetContextFields.vue'
diff --git a/src/components/screens/SearchVariantsScreen.vue b/src/components/screens/SearchVariantsScreen.vue
index aba122a6..6678fc13 100644
--- a/src/components/screens/SearchVariantsScreen.vue
+++ b/src/components/screens/SearchVariantsScreen.vue
@@ -778,7 +778,8 @@ import {
   getAlleleByGnomad,
   getGeneBySymbol
 } from '@/api/clingen'
-import {getCollection, getErrorResponse, lookupVariantsByClingenId} from '@/api/mavedb'
+import {getCollection, lookupVariantsByClingenId} from '@/api/mavedb'
+import {getErrorResponse} from '@/lib/errors'
 import {lookupVariantsByVrsDigest} from '@/api/mavedb/variants'
 import {useEntityCache} from '@/composables/entity-cache'
 import MvLoader from '@/components/common/MvLoader.vue'
diff --git a/src/components/screens/SettingsScreen.vue b/src/components/screens/SettingsScreen.vue
index ccd13d48..cade549b 100644
--- a/src/components/screens/SettingsScreen.vue
+++ b/src/components/screens/SettingsScreen.vue
@@ -153,15 +153,8 @@ import {defineComponent} from 'vue'
 import {useHead} from '@unhead/vue'
 import {useRouter} from 'vue-router'
 
-import {
-  createAccessKey,
-  createRoleAccessKey,
-  deleteAccessKey,
-  getErrorResponse,
-  getMyCollections,
-  searchMyExperiments,
-  searchMyScoreSets
-} from '@/api/mavedb'
+import {createAccessKey, createRoleAccessKey, deleteAccessKey, getMyCollections, searchMyExperiments, searchMyScoreSets} from '@/api/mavedb'
+import {getErrorResponse} from '@/lib/errors'
 import MvAccessKeyRow from '@/components/common/MvAccessKeyRow.vue'
 import MvOrcidLink from '@/components/common/MvOrcidLink.vue'
 import MvFloatField from '@/components/forms/MvFloatField.vue'
diff --git a/src/components/screens/VariantScreen.vue b/src/components/screens/VariantScreen.vue
index 14239880..8cae1126 100644
--- a/src/components/screens/VariantScreen.vue
+++ b/src/components/screens/VariantScreen.vue
@@ -3,21 +3,42 @@
     <template #header>
       <MvPageHeader eyebrow="Variant" max-width="1000px" :title="pageTitle">
         <template v-if="lookup.variants.value.length > 0" #actions>
-          <div class="hidden tablet:block">
+          <div class="hidden tablet:flex tablet:items-center tablet:gap-2">
             <SplitButton
-              :model="annotatedVariantDownloadOptions"
+              :disabled="downloadInProgress"
+              :model="tableDownloadMenu"
               severity="secondary"
               size="small"
-              @click="annotatedVariantDownloadOptions[0]?.command"
-            >
+              @click="primaryTableDownload.command()">
+              <template #default>
+                <i class="pi pi-table mr-1.5 text-xs" />
+                Download variant CSV
+              </template>
+            </SplitButton>
+            <SplitButton
+              v-if="annotationDownloadOptions.length > 0"
+              :disabled="downloadInProgress"
+              :model="annotationDownloadOptions"
+              severity="secondary"
+              size="small"
+              @click="primaryAnnotationDownload?.command()">
               <template #default>
                 <i class="pi pi-download mr-1.5 text-xs" />
-                Download annotations
+                Download VA-Spec annotations
               </template>
             </SplitButton>
+            <!-- Indeterminate: a gzipped download exposes no measurable total. -->
+            <span
+              v-if="downloadInProgress"
+              aria-live="polite"
+              class="flex items-center gap-1.5 text-xs text-text-muted">
+              <i class="pi pi-spin pi-spinner text-xs" />
+              Preparing {{ lookup.downloadInProgressLabel.value }}…
+            </span>
           </div>
           <MvRowActionMenu :actions="downloadActions" class="tablet:hidden" />
         </template>
+
         <template v-if="lookup.variants.value.length > 0" #subtitle>
           <p class="mt-2 text-sm text-text-muted">
             <template v-if="lookup.geneName.value">{{ lookup.geneName.value }} &middot; </template>
@@ -45,8 +66,7 @@
       <MvEmptyState
         v-else-if="lookup.variants.value.length === 0"
         description="No variants were found for this allele."
-        title="No variants found"
-      />
+        title="No variants found" />
 
       <template v-else>
         <!-- ── MEASUREMENTS SECTION ───────────────────────────── -->
@@ -64,8 +84,7 @@
                 active-border="var(--color-nucleotide-border)"
                 color="var(--color-nucleotide)"
                 :count="lookup.nucleotideCount.value"
-                label="Nucleotide level"
-              />
+                label="Nucleotide level" />
               <MvBadgeToggle
                 v-if="lookup.proteinCount.value > 0"
                 v-model="lookup.showProtein.value"
@@ -73,8 +92,7 @@
                 active-border="var(--color-protein-border)"
                 color="var(--color-protein)"
                 :count="lookup.proteinCount.value"
-                label="Protein level"
-              />
+                label="Protein level" />
               <MvBadgeToggle
                 v-if="lookup.associatedNucleotideCount.value > 0"
                 v-model="lookup.showAssociatedNucleotide.value"
@@ -82,8 +100,7 @@
                 active-border="var(--color-synonymous-nucleotide-border)"
                 color="var(--color-synonymous-nucleotide)"
                 :count="lookup.associatedNucleotideCount.value"
-                label="Synonymous nucleotide"
-              />
+                label="Synonymous nucleotide" />
             </div>
           </div>
           <!-- Desktop: horizontal scroll strip -->
@@ -101,8 +118,7 @@
               :normal-odds-path="lookup.getNormalOddsPath(variant.content.urn)"
               :study-title="variant.content.scoreSet?.title || 'Untitled score set'"
               :type="variant.type"
-              @select="lookup.selectVariant(variant.content.urn)"
-            />
+              @select="lookup.selectVariant(variant.content.urn)" />
           </div>
           <!-- Mobile: dropdown selector -->
           <div class="tablet:hidden px-4 py-3">
@@ -112,8 +128,7 @@
               option-label="label"
               option-value="urn"
               :options="measurementOptions"
-              @update:model-value="lookup.selectVariant($event)"
-            />
+              @update:model-value="lookup.selectVariant($event)" />
           </div>
         </div>
 
@@ -121,8 +136,7 @@
         <template v-if="lookup.selectedVariantDetail.value">
           <!-- Desktop: single card with two columns -->
           <div
-            class="mave-gradient-bar relative mt-6 hidden tablet:block rounded-lg border border-border bg-surface px-[18px] py-3.5"
-          >
+            class="mave-gradient-bar relative mt-6 hidden tablet:block rounded-lg border border-border bg-surface px-[18px] py-3.5">
             <div class="grid grid-cols-2">
               <div class="border-r border-border-light pr-[18px]">
                 <VariantInfoSection
@@ -130,47 +144,40 @@
                   :classification="lookup.calibrationResolution.classification.value"
                   :clingen-allele-id="lookup.selectedClingenAlleleId.value"
                   :clinvar-allele-ids="lookup.clingenAllele.clinvarAlleleIds.value"
-                  :genomic-locations="lookup.clingenAllele.genomicLocations.value"
-                />
+                  :genomic-locations="lookup.clingenAllele.genomicLocations.value" />
               </div>
               <div class="pl-[18px]">
                 <MvAssayFactsCard
                   :columns="1"
                   :score-set="lookup.selectedScoreSet.value ?? undefined"
-                  :variant-urn="lookup.selectedVariantDetail.value?.urn ?? undefined"
-                />
+                  :variant-urn="lookup.selectedVariantDetail.value?.urn ?? undefined" />
               </div>
             </div>
           </div>
 
           <!-- Mobile: separate cards -->
           <div
-            class="mt-6 tablet:hidden mave-gradient-bar relative rounded-lg border border-border bg-surface px-4 py-3.5"
-          >
+            class="mt-6 tablet:hidden mave-gradient-bar relative rounded-lg border border-border bg-surface px-4 py-3.5">
             <VariantInfoSection
               :allele-name="lookup.clingenAllele.alleleName.value"
               :classification="lookup.calibrationResolution.classification.value"
               :clingen-allele-id="lookup.selectedClingenAlleleId.value"
               :clinvar-allele-ids="lookup.clingenAllele.clinvarAlleleIds.value"
-              :genomic-locations="lookup.clingenAllele.genomicLocations.value"
-            />
+              :genomic-locations="lookup.clingenAllele.genomicLocations.value" />
           </div>
           <div
-            class="mt-4 tablet:hidden mave-gradient-bar relative rounded-lg border border-border bg-surface px-4 py-3.5"
-          >
+            class="mt-4 tablet:hidden mave-gradient-bar relative rounded-lg border border-border bg-surface px-4 py-3.5">
             <MvAssayFactsCard
               :columns="1"
               :score-set="lookup.selectedScoreSet.value ?? undefined"
-              :variant-urn="lookup.selectedVariantDetail.value?.urn ?? undefined"
-            />
+              :variant-urn="lookup.selectedVariantDetail.value?.urn ?? undefined" />
           </div>
         </template>
 
         <!-- ── ANNOTATIONS CARD ──────────────────────────────── -->
         <div
           v-if="lookup.selectedVariantDetail.value && lookup.selectedVariantScore.value != null"
-          class="mave-gradient-bar relative mt-6 rounded-lg border border-border bg-surface px-[18px] py-3.5"
-        >
+          class="mave-gradient-bar relative mt-6 rounded-lg border border-border bg-surface px-[18px] py-3.5">
           <div class="annotations-columns grid grid-cols-1 tablet:grid-cols-3">
             <!-- Classification -->
             <div class="tablet:pr-[18px]">
@@ -181,31 +188,26 @@
                   lookup.selectedVariantScore.value !== 'NA'
                     ? Number(lookup.selectedVariantScore.value).toPrecision(4)
                     : undefined
-                "
-              />
+                " />
               <MvDetailRow label="ACMG code">
                 <MvEvidenceTag
                   v-if="lookup.calibrationResolution.formattedEvidenceCode.value"
-                  :code="lookup.calibrationResolution.formattedEvidenceCode.value"
-                />
+                  :code="lookup.calibrationResolution.formattedEvidenceCode.value" />
               </MvDetailRow>
               <MvDetailRow
                 label="OddsPath ratio"
-                :value="lookup.calibrationResolution.scoreRange.value?.oddspathsRatio ?? undefined"
-              />
+                :value="lookup.calibrationResolution.scoreRange.value?.oddspathsRatio ?? undefined" />
             </div>
             <!-- Placeholder columns for future data -->
             <div
-              class="border-t border-border-light pt-4 tablet:border-t-0 tablet:pt-0 tablet:border-l tablet:border-border-light tablet:px-[18px]"
-            >
+              class="border-t border-border-light pt-4 tablet:border-t-0 tablet:pt-0 tablet:border-l tablet:border-border-light tablet:px-[18px]">
               <div class="mb-1.5 text-xs-minus font-bold uppercase tracking-[0.5px] text-black">
                 Population Frequency
               </div>
               <p class="text-xs-plus italic text-text-muted">Data coming soon</p>
             </div>
             <div
-              class="border-t border-border-light pt-4 tablet:border-t-0 tablet:pt-0 tablet:border-l tablet:border-border-light tablet:pl-[18px]"
-            >
+              class="border-t border-border-light pt-4 tablet:border-t-0 tablet:pt-0 tablet:border-l tablet:border-border-light tablet:pl-[18px]">
               <div class="mb-1.5 text-xs-minus font-bold uppercase tracking-[0.5px] text-black">
                 Splicing Predictions
               </div>
@@ -217,8 +219,7 @@
         <!-- ── SCORE DISTRIBUTION CHART ──────────────────────── -->
         <div v-if="lookup.selectedScoreSet.value" class="mt-6 rounded-lg border border-border bg-surface">
           <div
-            class="flex flex-wrap items-center justify-between gap-3 border-b border-border-light px-4 tablet:px-5 py-3.5"
-          >
+            class="flex flex-wrap items-center justify-between gap-3 border-b border-border-light px-4 tablet:px-5 py-3.5">
             <div class="min-w-0">
               <router-link
                 class="text-base tablet:text-lg font-bold text-link"
@@ -226,8 +227,7 @@
                   name: 'scoreSet',
                   params: {urn: lookup.selectedScoreSet.value.urn},
                   query: {variant: lookup.selectedVariantDetail.value?.urn}
-                }"
-              >
+                }">
                 {{ lookup.selectedScoreSet.value.title }}
               </router-link>
             </div>
@@ -244,8 +244,7 @@
                 :selected-calibration="lookup.selectedCalibration.value || undefined"
                 :variants="lookup.scores.value"
                 @calibration-changed="lookup.selectedCalibration.value = $event"
-                @selection-changed="() => {}"
-              />
+                @selection-changed="() => {}" />
             </div>
             <div v-else class="flex min-h-[200px] items-center justify-center">
               <MvLoader text="Loading variant information..." />
@@ -254,12 +253,17 @@
           <div v-if="lookup.selectedCalibrationObject.value" class="border-t border-border-light p-5">
             <CalibrationTable
               :highlighted-range-label="lookup.calibrationResolution.scoreRange.value?.label || null"
-              :score-calibration="lookup.selectedCalibrationObject.value"
-            />
+              :score-calibration="lookup.selectedCalibrationObject.value" />
           </div>
         </div>
       </template>
     </div>
+    <MvCsvColumnDialog
+      v-model:visible="csvDialogVisible"
+      header="Download clinical table"
+      kind="variant"
+      :urn="lookup.selectedVariantUrn.value"
+      @confirm="downloadSelectedCsv" />
   </MvLayout>
 </template>
 
@@ -280,6 +284,7 @@ import MvPageLoading from '@/components/common/MvPageLoading.vue'
 import MvLayout from '@/components/layout/MvLayout.vue'
 import MvPageHeader from '@/components/layout/MvPageHeader.vue'
 import MvAssayFactsCard from '@/components/common/MvAssayFactsCard.vue'
+import MvCsvColumnDialog from '@/components/common/MvCsvColumnDialog.vue'
 import MvBadgeToggle from '@/components/common/MvBadgeToggle.vue'
 import ScoreSetHistogram from '@/components/score-set/ScoreSetHistogram.vue'
 import MvMeasurementCard from '@/components/variant/MvMeasurementCard.vue'
@@ -289,6 +294,12 @@ import {useVariantLookup} from '@/composables/use-variant-lookup'
 import {MEASUREMENT_TYPE_LABELS} from '@/lib/measurement-types'
 import {hasFunctionalCalibrations, hasPathogenicityCalibrations} from '@/lib/calibrations'
 
+/** One entry in a download control: a label and the download it triggers. */
+interface DownloadOption {
+  label: string
+  command: () => void
+}
+
 export default defineComponent({
   name: 'VariantScreen',
 
@@ -306,6 +317,7 @@ export default defineComponent({
     MvPageHeader,
     MvRowActionMenu,
     MvPageLoading,
+    MvCsvColumnDialog,
     PSelect: Select,
     ScoreSetHistogram,
     SplitButton,
@@ -326,7 +338,17 @@ export default defineComponent({
     }
   },
 
+  data() {
+    return {
+      csvDialogVisible: false
+    }
+  },
+
   computed: {
+    /** Any download in flight; the buttons stay disabled until it settles. */
+    downloadInProgress(): boolean {
+      return this.lookup.downloadInProgressLabel.value !== null
+    },
     pageTitle(): string {
       return this.lookup.clingenAllele.alleleName.value || this.lookup.selectedVariantName.value || 'Variant'
     },
@@ -338,14 +360,44 @@ export default defineComponent({
           urn: variant.content.urn
         }))
     },
-    downloadActions(): RowAction[] {
-      return this.annotatedVariantDownloadOptions.map((opt) => ({
-        label: opt.label,
-        handler: opt.command
-      }))
+    /**
+     * The flat table download: one CSV of this allele's measurements.
+     *
+     * Always offered. Unlike the VA-Spec objects it needs no mapping, score, or calibration — an
+     * unmapped variant still has an identity, a score, and provenance worth exporting.
+     */
+    tableDownloadOptions(): DownloadOption[] {
+      return [
+        {label: 'Download variant CSV', command: () => this.lookup.downloadVariantCsvFile()},
+        {
+          label: 'Choose CSV columns…',
+          command: () => {
+            this.csvDialogVisible = true
+          }
+        }
+      ]
+    },
+
+    /** What clicking the table button itself does: download with the default column set. */
+    primaryTableDownload(): DownloadOption {
+      return this.tableDownloadOptions[0]
+    },
+
+    /** What its caret offers: everything beyond the one-click default. */
+    tableDownloadMenu(): DownloadOption[] {
+      return this.tableDownloadOptions.slice(1)
     },
-    annotatedVariantDownloadOptions(): {label: string; command: () => void}[] {
-      const options: {label: string; command: () => void}[] = []
+
+    /**
+     * The VA-Spec downloads: nested, standards-compliant annotation objects.
+     *
+     * A different product from the table — machine-readable GA4GH structures rather than something to
+     * open in a spreadsheet — so they get their own control rather than sharing a menu. Each requires
+     * progressively more of the variant to exist, so the list is empty for an unmapped variant and the
+     * button is hidden entirely.
+     */
+    annotationDownloadOptions(): DownloadOption[] {
+      const options: DownloadOption[] = []
       const activeVariant = this.lookup.selectedVariantDetail.value
       if (!activeVariant) return options
 
@@ -375,6 +427,21 @@ export default defineComponent({
       }
 
       return options
+    },
+
+    /** What clicking the annotations button itself does: the highest-level statement available. */
+    primaryAnnotationDownload(): DownloadOption | undefined {
+      return this.annotationDownloadOptions[0]
+    },
+
+    /** The narrow-screen equivalent: both groups in one menu, separated so they stay distinguishable. */
+    downloadActions(): RowAction[] {
+      const asAction = (option: DownloadOption): RowAction => ({label: option.label, handler: option.command})
+      const annotations = this.annotationDownloadOptions
+      return [
+        ...this.tableDownloadOptions.map(asAction),
+        ...(annotations.length > 0 ? [{separator: true} as RowAction, ...annotations.map(asAction)] : [])
+      ]
     }
   },
 
@@ -384,7 +451,11 @@ export default defineComponent({
     }
   },
 
-  methods: {}
+  methods: {
+    downloadSelectedCsv({namespaces}: {namespaces: string[]}) {
+      this.lookup.downloadVariantCsvFile(namespaces)
+    }
+  }
 })
 </script>
 
diff --git a/src/composables/use-csv-namespaces.test.ts b/src/composables/use-csv-namespaces.test.ts
new file mode 100644
index 00000000..95261021
--- /dev/null
+++ b/src/composables/use-csv-namespaces.test.ts
@@ -0,0 +1,559 @@
+import {CanceledError} from 'axios'
+import {beforeEach, describe, expect, it, vi} from 'vitest'
+import {ref} from 'vue'
+
+import {useCsvNamespaces, type AvailableCsvNamespace, type CsvNamespaceSection} from './use-csv-namespaces'
+
+const getScoreSetCsvNamespaces = vi.fn()
+const getVariantCsvNamespaces = vi.fn()
+
+vi.mock('@/api/mavedb', () => ({
+  getScoreSetCsvNamespaces: (...args: unknown[]) => getScoreSetCsvNamespaces(...args),
+  getVariantCsvNamespaces: (...args: unknown[]) => getVariantCsvNamespaces(...args)
+}))
+
+function entry(
+  overrides: Partial<AvailableCsvNamespace> & {
+    selectedByDefault?: boolean
+    scoreSet?: {urn: string; title: string}
+  }
+): AvailableCsvNamespace {
+  return {
+    namespace: 'scores',
+    label: 'Scores',
+    group: 'data',
+    ...overrides
+  } as AvailableCsvNamespace
+}
+
+const SCORE_SET_ENTRIES: AvailableCsvNamespace[] = [
+  entry({namespace: 'scores', label: 'Scores', group: 'data'}),
+  entry({namespace: 'gnomad', label: 'gnomAD allele frequency', group: 'annotation'}),
+  entry({namespace: 'clinvar.2024_11', label: 'ClinVar significance (November 2024)', group: 'annotation'}),
+  entry({namespace: 'calibration.urn:mavedb:calibration-1', label: 'Brnich et al. 2019', group: 'calibration'}),
+  entry({namespace: 'score_set', label: 'Score set and publications', group: 'provenance'})
+]
+
+beforeEach(() => {
+  getScoreSetCsvNamespaces.mockReset()
+  getVariantCsvNamespaces.mockReset()
+})
+
+describe('useCsvNamespaces', () => {
+  it('does not fetch until load is called', () => {
+    useCsvNamespaces({urn: ref('urn:mavedb:00000001-a-1'), kind: 'scoreSet'})
+
+    expect(getScoreSetCsvNamespaces).not.toHaveBeenCalled()
+  })
+
+  it('loads score set namespaces from the score set endpoint', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValue(SCORE_SET_ENTRIES)
+    const {namespaces, load} = useCsvNamespaces({urn: ref('urn:mavedb:00000001-a-1'), kind: 'scoreSet'})
+
+    await load()
+
+    expect(getScoreSetCsvNamespaces).toHaveBeenCalledOnce()
+    expect(getVariantCsvNamespaces).not.toHaveBeenCalled()
+    expect(namespaces.value).toHaveLength(5)
+  })
+
+  it('loads variant namespaces from the variant endpoint', async () => {
+    getVariantCsvNamespaces.mockResolvedValue(SCORE_SET_ENTRIES)
+    const {load} = useCsvNamespaces({urn: ref('urn:mavedb:00000001-a-1#1'), kind: 'variant'})
+
+    await load()
+
+    expect(getVariantCsvNamespaces).toHaveBeenCalledOnce()
+    expect(getScoreSetCsvNamespaces).not.toHaveBeenCalled()
+  })
+
+  it('groups namespaces into ordered sections, omitting empty ones', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValue(SCORE_SET_ENTRIES)
+    const {sections, load} = useCsvNamespaces({urn: ref('urn:mavedb:00000001-a-1'), kind: 'scoreSet'})
+
+    await load()
+
+    expect(sections.value.map((section) => section.group)).toEqual(['data', 'annotation', 'calibration', 'provenance'])
+    expect(sections.value[1].namespaces.map((entry) => entry.namespace)).toEqual(['gnomad', 'clinvar.2024_11'])
+    expect(sections.value[2].title).toBe('Clinical interpretation')
+  })
+
+  it('omits sections with no namespaces', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValue([entry({namespace: 'scores', group: 'data'})])
+    const {sections, load} = useCsvNamespaces({urn: ref('urn:mavedb:00000001-a-1'), kind: 'scoreSet'})
+
+    await load()
+
+    expect(sections.value.map((section) => section.group)).toEqual(['data'])
+  })
+
+  it('serves labels from the API rather than deriving them', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValue(SCORE_SET_ENTRIES)
+    const {namespaces, load} = useCsvNamespaces({urn: ref('urn:mavedb:00000001-a-1'), kind: 'scoreSet'})
+
+    await load()
+
+    const calibration = namespaces.value.find((n) => n.namespace.startsWith('calibration.'))
+    expect(calibration?.label).toBe('Brnich et al. 2019')
+    const clinvar = namespaces.value.find((n) => n.namespace.startsWith('clinvar.'))
+    expect(clinvar?.label).toBe('ClinVar significance (November 2024)')
+  })
+
+  it('caches per URN so reopening a dialog does not refetch', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValue(SCORE_SET_ENTRIES)
+    const {load} = useCsvNamespaces({urn: ref('urn:mavedb:00000001-a-1'), kind: 'scoreSet'})
+
+    await load()
+    await load()
+
+    expect(getScoreSetCsvNamespaces).toHaveBeenCalledOnce()
+  })
+
+  it('refetches when the URN changes', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValue(SCORE_SET_ENTRIES)
+    const urn = ref('urn:mavedb:00000001-a-1')
+    const {load} = useCsvNamespaces({urn, kind: 'scoreSet'})
+
+    await load()
+    urn.value = 'urn:mavedb:00000001-a-2'
+    await load()
+
+    expect(getScoreSetCsvNamespaces).toHaveBeenCalledTimes(2)
+  })
+
+  it('does not fetch without a URN', async () => {
+    const {load} = useCsvNamespaces({urn: ref(null), kind: 'scoreSet'})
+
+    await load()
+
+    expect(getScoreSetCsvNamespaces).not.toHaveBeenCalled()
+  })
+
+  it('reports an error and offers nothing when the request fails', async () => {
+    getScoreSetCsvNamespaces.mockRejectedValue(new Error('boom'))
+    const {namespaces, hasNamespaces, error, loading, load} = useCsvNamespaces({
+      urn: ref('urn:mavedb:00000001-a-1'),
+      kind: 'scoreSet'
+    })
+
+    await load()
+
+    expect(error.value).toBeTruthy()
+    expect(namespaces.value).toEqual([])
+    expect(hasNamespaces.value).toBe(false)
+    expect(loading.value).toBe(false)
+  })
+
+  it('retries after a failure rather than caching the empty result', async () => {
+    getScoreSetCsvNamespaces.mockRejectedValueOnce(new Error('boom')).mockResolvedValue(SCORE_SET_ENTRIES)
+    const {hasNamespaces, error, load} = useCsvNamespaces({urn: ref('urn:mavedb:00000001-a-1'), kind: 'scoreSet'})
+
+    await load()
+    await load()
+
+    expect(getScoreSetCsvNamespaces).toHaveBeenCalledTimes(2)
+    expect(error.value).toBeNull()
+    expect(hasNamespaces.value).toBe(true)
+  })
+
+  it('ignores an aborted request instead of reporting it as an error', async () => {
+    getScoreSetCsvNamespaces.mockRejectedValue(new CanceledError('canceled'))
+    const {error, load} = useCsvNamespaces({urn: ref('urn:mavedb:00000001-a-1'), kind: 'scoreSet'})
+
+    await load()
+
+    expect(error.value).toBeNull()
+  })
+
+  it('a superseded request neither clears the spinner nor drops the live request', async () => {
+    // The abort lands while the second request is still in flight. If the first one's cleanup ran
+    // unguarded, the dialog would stop showing a spinner and reset() could no longer abort what is
+    // actually loading.
+    let resolveSecond: (entries: AvailableCsvNamespace[]) => void = () => {}
+    getScoreSetCsvNamespaces
+      .mockRejectedValueOnce(new CanceledError('canceled'))
+      .mockReturnValueOnce(new Promise((resolve) => (resolveSecond = resolve)))
+
+    const urn = ref('urn:mavedb:00000001-a-1')
+    const {hasNamespaces, loading, load, reset} = useCsvNamespaces({urn, kind: 'scoreSet'})
+
+    const first = load()
+    urn.value = 'urn:mavedb:00000001-a-2'
+    const second = load()
+    await first
+
+    expect(loading.value).toBe(true)
+
+    reset()
+    resolveSecond(SCORE_SET_ENTRIES)
+    await second
+
+    // reset() aborted the live request, so its result must not land after the fact.
+    expect(hasNamespaces.value).toBe(false)
+  })
+
+  it('does not count a formatting extra as a column group', async () => {
+    // The Download button is enabled from this count, and a formatting flag produces no columns — that is
+    // how an empty `namespaces` request used to slip through and come back as the API's default.
+    getScoreSetCsvNamespaces.mockResolvedValue(SCORE_SET_ENTRIES)
+    const extraOptions = ref([{label: "Omit HGVS columns this score set doesn't use", value: 'dropUnusedHgvs'}])
+    const {selected, selectedExtras, selectedColumnGroups, load} = useCsvNamespaces({
+      urn: ref('urn:mavedb:00000001-a-1'),
+      kind: 'scoreSet',
+      extraOptions
+    })
+
+    await load()
+    selected.value = []
+    selectedExtras.value = ['dropUnusedHgvs']
+
+    expect(selectedColumnGroups.value).toBe(0)
+  })
+
+  it('reset clears loaded namespaces', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValue(SCORE_SET_ENTRIES)
+    const {hasNamespaces, load, reset} = useCsvNamespaces({urn: ref('urn:mavedb:00000001-a-1'), kind: 'scoreSet'})
+
+    await load()
+    expect(hasNamespaces.value).toBe(true)
+
+    reset()
+
+    expect(hasNamespaces.value).toBe(false)
+  })
+})
+
+describe('useCsvNamespaces selection', () => {
+  it('selects everything once the list loads', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValue(SCORE_SET_ENTRIES)
+    const {selected, allSelected, load} = useCsvNamespaces({urn: ref('urn:mavedb:00000001-a-1'), kind: 'scoreSet'})
+
+    await load()
+
+    expect(allSelected.value).toBe(true)
+    expect(selected.value).toEqual(SCORE_SET_ENTRIES.map((entry) => entry.namespace))
+  })
+
+  it('starts with nothing selected before loading', () => {
+    const {selected, allSelected} = useCsvNamespaces({urn: ref('urn:mavedb:00000001-a-1'), kind: 'scoreSet'})
+
+    expect(selected.value).toEqual([])
+    expect(allSelected.value).toBe(false)
+  })
+
+  it('toggleAll clears a full selection', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValue(SCORE_SET_ENTRIES)
+    const {selected, allSelected, toggleAll, load} = useCsvNamespaces({
+      urn: ref('urn:mavedb:00000001-a-1'),
+      kind: 'scoreSet'
+    })
+    await load()
+
+    toggleAll()
+
+    expect(selected.value).toEqual([])
+    expect(allSelected.value).toBe(false)
+  })
+
+  it('toggleAll restores everything from an empty selection', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValue(SCORE_SET_ENTRIES)
+    const {selected, toggleAll, load} = useCsvNamespaces({urn: ref('urn:mavedb:00000001-a-1'), kind: 'scoreSet'})
+    await load()
+
+    toggleAll()
+    toggleAll()
+
+    expect(selected.value).toHaveLength(SCORE_SET_ENTRIES.length)
+  })
+
+  it('toggleAll selects everything from a partial selection', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValue(SCORE_SET_ENTRIES)
+    const {selected, toggleAll, load} = useCsvNamespaces({urn: ref('urn:mavedb:00000001-a-1'), kind: 'scoreSet'})
+    await load()
+    selected.value = ['scores']
+
+    toggleAll()
+
+    expect(selected.value).toHaveLength(SCORE_SET_ENTRIES.length)
+  })
+
+  it('keeps a narrowed selection when the dialog is reopened for the same record', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValue(SCORE_SET_ENTRIES)
+    const {selected, load} = useCsvNamespaces({urn: ref('urn:mavedb:00000001-a-1'), kind: 'scoreSet'})
+    await load()
+    selected.value = ['scores']
+
+    await load()
+
+    expect(selected.value).toEqual(['scores'])
+  })
+
+  it('reselects everything when the record changes', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValue(SCORE_SET_ENTRIES)
+    const urn = ref('urn:mavedb:00000001-a-1')
+    const {selected, load} = useCsvNamespaces({urn, kind: 'scoreSet'})
+    await load()
+    selected.value = ['scores']
+
+    urn.value = 'urn:mavedb:00000001-a-2'
+    await load()
+
+    expect(selected.value).toHaveLength(SCORE_SET_ENTRIES.length)
+  })
+
+  it('clears the selection when loading fails', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValueOnce(SCORE_SET_ENTRIES).mockRejectedValueOnce(new Error('boom'))
+    const urn = ref('urn:mavedb:00000001-a-1')
+    const {selected, load} = useCsvNamespaces({urn, kind: 'scoreSet'})
+    await load()
+
+    urn.value = 'urn:mavedb:00000001-a-2'
+    await load()
+
+    expect(selected.value).toEqual([])
+  })
+
+  it('summarizes the selection so the picker states it outright', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValue(SCORE_SET_ENTRIES)
+    const {selected, selectionSummary, load} = useCsvNamespaces({
+      urn: ref('urn:mavedb:00000001-a-1'),
+      kind: 'scoreSet'
+    })
+    await load()
+    expect(selectionSummary.value).toBe('All columns selected')
+
+    selected.value = ['scores', 'gnomad']
+    expect(selectionSummary.value).toBe('2 of 5 column groups selected')
+
+    selected.value = []
+    expect(selectionSummary.value).toBe('No columns selected')
+  })
+})
+
+describe('useCsvNamespaces default selection', () => {
+  const WITH_RESEARCH_USE_ONLY: AvailableCsvNamespace[] = [
+    entry({namespace: 'scores', label: 'Scores', group: 'data'}),
+    entry({
+      namespace: 'calibration.urn:mavedb:calibration-1',
+      label: 'Brnich et al. 2019',
+      group: 'calibration'
+    }),
+    entry({
+      namespace: 'calibration.urn:mavedb:calibration-2',
+      label: 'Research Use Only: Provisional',
+      group: 'calibration',
+      selectedByDefault: false
+    })
+  ]
+
+  it('leaves research-use-only calibrations unchecked on load', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValue(WITH_RESEARCH_USE_ONLY)
+    const {selected, load} = useCsvNamespaces({urn: ref('urn:mavedb:00000001-a-1'), kind: 'scoreSet'})
+
+    await load()
+
+    expect(selected.value).toEqual(['scores', 'calibration.urn:mavedb:calibration-1'])
+  })
+
+  it('still offers them, so a user can opt in', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValue(WITH_RESEARCH_USE_ONLY)
+    const {namespaces, sections, load} = useCsvNamespaces({urn: ref('urn:mavedb:00000001-a-1'), kind: 'scoreSet'})
+
+    await load()
+
+    expect(namespaces.value).toHaveLength(3)
+    const calibrationSection = sections.value.find((section) => section.group === 'calibration')
+    expect(calibrationSection?.namespaces.map((entry) => entry.label)).toContain('Research Use Only: Provisional')
+  })
+
+  it('is not fully selected on load when a group is excluded by default', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValue(WITH_RESEARCH_USE_ONLY)
+    const {allSelected, selectionSummary, load} = useCsvNamespaces({
+      urn: ref('urn:mavedb:00000001-a-1'),
+      kind: 'scoreSet'
+    })
+
+    await load()
+
+    expect(allSelected.value).toBe(false)
+    expect(selectionSummary.value).toBe('2 of 3 column groups selected')
+  })
+
+  it('select all reaches research-use-only groups, since that is an explicit act', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValue(WITH_RESEARCH_USE_ONLY)
+    const {selected, allSelected, toggleAll, load} = useCsvNamespaces({
+      urn: ref('urn:mavedb:00000001-a-1'),
+      kind: 'scoreSet'
+    })
+    await load()
+
+    toggleAll()
+
+    expect(allSelected.value).toBe(true)
+    expect(selected.value).toContain('calibration.urn:mavedb:calibration-2')
+  })
+})
+
+describe('useCsvNamespaces extras', () => {
+  const NAMESPACE_ENTRIES: AvailableCsvNamespace[] = [
+    entry({namespace: 'scores', label: 'Score', group: 'data'}),
+    entry({namespace: 'scores_custom', label: 'Investigator-provided score columns', group: 'data'}),
+    entry({namespace: 'gnomad', label: 'gnomAD allele frequency', group: 'annotation'})
+  ]
+
+  const EXTRAS = [{label: "Omit HGVS columns this score set doesn't use", value: 'dropUnusedHgvsColumns'}]
+
+  function withExtras() {
+    return useCsvNamespaces({
+      urn: ref('urn:mavedb:00000001-a-1'),
+      kind: 'scoreSet',
+      extraOptions: ref(EXTRAS)
+    })
+  }
+
+  it('counts only namespaces as column groups', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValue(NAMESPACE_ENTRIES)
+    const {totalColumnGroups, load} = withExtras()
+
+    await load()
+
+    // The investigator's score columns are a namespace now, so all three count; the flag does not.
+    expect(totalColumnGroups.value).toBe(3)
+  })
+
+  it('treats the investigator score columns as an ordinary namespace', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValue(NAMESPACE_ENTRIES)
+    const {selected, load} = withExtras()
+
+    await load()
+
+    expect(selected.value).toContain('scores')
+    expect(selected.value).toContain('scores_custom')
+  })
+
+  it('is still "all selected" while a formatting extra is unchecked', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValue(NAMESPACE_ENTRIES)
+    const {selectedExtras, allSelected, load} = withExtras()
+    await load()
+
+    selectedExtras.value = []
+
+    expect(allSelected.value).toBe(true)
+  })
+
+  it('leaves formatting extras unchecked on load', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValue(NAMESPACE_ENTRIES)
+    const {selectedExtras, load} = withExtras()
+
+    await load()
+
+    expect(selectedExtras.value).toEqual([])
+  })
+
+  it('select all does not disturb formatting options', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValue(NAMESPACE_ENTRIES)
+    const {selectedExtras, toggleAll, load} = withExtras()
+    await load()
+    selectedExtras.value = ['dropUnusedHgvsColumns']
+
+    toggleAll()
+    toggleAll()
+
+    expect(selectedExtras.value).toEqual(['dropUnusedHgvsColumns'])
+  })
+
+  it('exposes formatting options for the Options section', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValue(NAMESPACE_ENTRIES)
+    const {formattingExtraOptions, load} = withExtras()
+
+    await load()
+
+    expect(formattingExtraOptions.value.map((o) => o.value)).toEqual(['dropUnusedHgvsColumns'])
+  })
+})
+
+describe('useCsvNamespaces score set subdivision', () => {
+  const ONE_SCORE_SET: AvailableCsvNamespace[] = [
+    entry({namespace: 'scores', group: 'data'}),
+    entry({
+      namespace: 'calibration.urn:mavedb:calibration-1',
+      label: 'First Assay Calibration',
+      group: 'calibration',
+      scoreSet: {urn: 'urn:mavedb:00000001-a-1', title: 'First Assay'}
+    })
+  ]
+
+  const TWO_SCORE_SETS: AvailableCsvNamespace[] = [
+    ...ONE_SCORE_SET,
+    entry({
+      namespace: 'calibration.urn:mavedb:calibration-2',
+      label: 'Second Assay Calibration',
+      group: 'calibration',
+      scoreSet: {urn: 'urn:mavedb:00000001-a-2', title: 'Second Assay'}
+    })
+  ]
+
+  function sectionFor(sections: CsvNamespaceSection[], group: string) {
+    return sections.find((section) => section.group === group)
+  }
+
+  it('does not subdivide when only one score set is represented', async () => {
+    getScoreSetCsvNamespaces.mockResolvedValue(ONE_SCORE_SET)
+    const {sections, load} = useCsvNamespaces({urn: ref('urn:mavedb:00000001-a-1'), kind: 'scoreSet'})
+
+    await load()
+
+    const calibrations = sectionFor(sections.value, 'calibration')
+    expect(calibrations?.subsections).toHaveLength(1)
+    expect(calibrations?.subsections[0].label).toBeNull()
+  })
+
+  it('subdivides by score set once more than one is represented', async () => {
+    getVariantCsvNamespaces.mockResolvedValue(TWO_SCORE_SETS)
+    const {sections, load} = useCsvNamespaces({urn: ref('urn:mavedb:00000001-a-1#1'), kind: 'variant'})
+
+    await load()
+
+    const calibrations = sectionFor(sections.value, 'calibration')
+    // Headed by title, not URN — but the URN comes along for disambiguation.
+    expect(calibrations?.subsections.map((s) => s.label)).toEqual(['First Assay', 'Second Assay'])
+    expect(calibrations?.subsections.map((s) => s.urn)).toEqual(['urn:mavedb:00000001-a-1', 'urn:mavedb:00000001-a-2'])
+    expect(calibrations?.subsections[0].namespaces.map((e) => e.label)).toEqual(['First Assay Calibration'])
+    expect(calibrations?.subsections[1].namespaces.map((e) => e.label)).toEqual(['Second Assay Calibration'])
+  })
+
+  it('never subdivides sections whose namespaces have no owning score set', async () => {
+    getVariantCsvNamespaces.mockResolvedValue(TWO_SCORE_SETS)
+    const {sections, load} = useCsvNamespaces({urn: ref('urn:mavedb:00000001-a-1#1'), kind: 'variant'})
+
+    await load()
+
+    const data = sectionFor(sections.value, 'data')
+    expect(data?.subsections).toHaveLength(1)
+    expect(data?.subsections[0].label).toBeNull()
+  })
+
+  it('keeps the flat list alongside the subdivision', async () => {
+    getVariantCsvNamespaces.mockResolvedValue(TWO_SCORE_SETS)
+    const {sections, load} = useCsvNamespaces({urn: ref('urn:mavedb:00000001-a-1#1'), kind: 'variant'})
+
+    await load()
+
+    const calibrations = sectionFor(sections.value, 'calibration')
+    expect(calibrations?.namespaces).toHaveLength(2)
+    expect(calibrations?.subsections.flatMap((s) => s.namespaces)).toHaveLength(2)
+  })
+
+  it('still selects everything by default across score sets', async () => {
+    getVariantCsvNamespaces.mockResolvedValue(TWO_SCORE_SETS)
+    const {selected, allSelected, load} = useCsvNamespaces({
+      urn: ref('urn:mavedb:00000001-a-1#1'),
+      kind: 'variant'
+    })
+
+    await load()
+
+    expect(allSelected.value).toBe(true)
+    expect(selected.value).toHaveLength(3)
+  })
+})
diff --git a/src/composables/use-csv-namespaces.ts b/src/composables/use-csv-namespaces.ts
new file mode 100644
index 00000000..6ee757bf
--- /dev/null
+++ b/src/composables/use-csv-namespaces.ts
@@ -0,0 +1,220 @@
+import axios from 'axios'
+import {computed, ref, type Ref} from 'vue'
+
+import {getScoreSetCsvNamespaces, getVariantCsvNamespaces} from '@/api/mavedb'
+import type {components} from '@/schema/openapi'
+
+export type AvailableCsvNamespace = components['schemas']['AvailableCsvNamespace']
+export type CsvNamespaceGroup = components['schemas']['CsvNamespaceGroup']
+
+/** Section headings for a namespace picker, in the order they should be shown. */
+const GROUP_ORDER: CsvNamespaceGroup[] = ['data', 'annotation', 'calibration', 'provenance']
+
+const GROUP_TITLES: Record<CsvNamespaceGroup, string> = {
+  data: 'Measurements',
+  annotation: 'Annotations',
+  calibration: 'Clinical interpretation',
+  provenance: 'Provenance'
+}
+
+export interface CsvNamespaceSubsection {
+  /** A heading for this run of namespaces, or null when the section needs no subdivision. */
+  label: string | null
+  /** The URN behind the heading, for a tooltip or secondary text. Null when there is no heading. */
+  urn: string | null
+  namespaces: AvailableCsvNamespace[]
+}
+
+export interface CsvNamespaceSection {
+  group: CsvNamespaceGroup
+  title: string
+  /** Every namespace in the section, regardless of subdivision. */
+  namespaces: AvailableCsvNamespace[]
+  /**
+   * The namespaces split by owning score set, when more than one is represented; otherwise a single
+   * null-labelled subsection that renders as an undivided list. A variant's calibrations can span score
+   * sets, and one means nothing against another's scores.
+   */
+  subsections: CsvNamespaceSubsection[]
+}
+
+/**
+ * Split a section's namespaces by owning score set, but only when more than one is represented.
+ * Headings use the title; the URN comes along for disambiguation, since titles can collide.
+ */
+function subdivideByScoreSet(namespaces: AvailableCsvNamespace[]): CsvNamespaceSubsection[] {
+  const owners = new Map<string, string>()
+  for (const entry of namespaces) {
+    if (entry.scoreSet) owners.set(entry.scoreSet.urn, entry.scoreSet.title)
+  }
+  if (owners.size < 2) return [{label: null, urn: null, namespaces}]
+
+  const subsections = [...owners.entries()]
+    .sort(([, titleA], [, titleB]) => titleA.localeCompare(titleB))
+    .map(([urn, title]) => ({
+      label: title,
+      urn,
+      namespaces: namespaces.filter((entry) => entry.scoreSet?.urn === urn)
+    }))
+
+  // Anything without an owner still has to appear somewhere.
+  const unowned = namespaces.filter((entry) => !entry.scoreSet)
+  return unowned.length > 0 ? [...subsections, {label: null, urn: null, namespaces: unowned}] : subsections
+}
+
+/** A query flag that is not a column group, rendered under "Options" and returned as an `extra`. */
+export interface CsvExtraOption {
+  label: string
+  value: string
+}
+
+interface UseCsvNamespacesOptions {
+  /** The record whose namespaces to offer. Not watched; `load()` refetches when it sees a new URN. */
+  urn: Ref<string | null | undefined>
+  /** Which endpoint to ask. Variants widen over equivalent measurements; score sets do not. */
+  kind: 'scoreSet' | 'variant'
+  /** Formatting flags. Which ones an endpoint accepts is the caller's business. */
+  extraOptions?: Ref<CsvExtraOption[]>
+}
+
+/**
+ * Load the CSV column namespaces a record has data for, ready to render as a picker.
+ *
+ * Fetched lazily — call `load()` when a dialog opens — and cached per URN. Labels and grouping come from
+ * the API, which alone knows calibration titles and release dates.
+ */
+export function useCsvNamespaces({urn, kind, extraOptions}: UseCsvNamespacesOptions) {
+  const namespaces = ref<AvailableCsvNamespace[]>([])
+  const loading = ref(false)
+  const error = ref<string | null>(null)
+  const loadedUrn = ref<string | null>(null)
+  const controller = ref<AbortController | null>(null)
+  const selected = ref<string[]>([])
+  const selectedExtras = ref<string[]>([])
+
+  const formattingExtraOptions = computed(() => extraOptions?.value ?? [])
+
+  const sections = computed<CsvNamespaceSection[]>(() =>
+    GROUP_ORDER.map((group) => {
+      const inGroup = namespaces.value.filter((entry) => entry.group === group)
+      return {
+        group,
+        title: GROUP_TITLES[group],
+        namespaces: inGroup,
+        subsections: subdivideByScoreSet(inGroup)
+      }
+    }).filter((section) => section.namespaces.length > 0)
+  )
+
+  /** Whether the record has anything at all to offer. False while loading and on error. */
+  const hasNamespaces = computed(() => namespaces.value.length > 0)
+
+  /** Column groups on offer. Only namespaces count; checking an extra alone produces no file. */
+  const totalColumnGroups = computed(() => namespaces.value.length)
+
+  const selectedColumnGroups = computed(() => selected.value.length)
+
+  const allSelected = computed(
+    () => totalColumnGroups.value > 0 && selectedColumnGroups.value === totalColumnGroups.value
+  )
+
+  /** Describes the current selection, so the picker never has to explain an implicit rule. */
+  const selectionSummary = computed(() => {
+    if (selectedColumnGroups.value === 0) return 'No columns selected'
+    if (allSelected.value) return 'All columns selected'
+    return `${selectedColumnGroups.value} of ${totalColumnGroups.value} column groups selected`
+  })
+
+  /** Formatting options are left alone: "Select all" is about columns. */
+  function selectAll(): void {
+    selected.value = namespaces.value.map((entry) => entry.namespace)
+  }
+
+  /**
+   * Select the groups the API marks as defaults, and every refinement of them. Research-use-only and
+   * rangeless calibrations are offered but excluded, so checking one is a deliberate act.
+   */
+  function selectDefaults(): void {
+    selected.value = namespaces.value
+      .filter((entry) => entry.selectedByDefault !== false)
+      .map((entry) => entry.namespace)
+  }
+
+  /** Select everything, or clear when everything is already selected. */
+  function toggleAll(): void {
+    if (!allSelected.value) {
+      selectAll()
+      return
+    }
+    selected.value = []
+  }
+
+  async function load(): Promise<void> {
+    if (!urn.value) return
+    // Already have this record's list; a namespace set only changes when the record does.
+    if (loadedUrn.value === urn.value && namespaces.value.length > 0) return
+
+    controller.value?.abort()
+    // Held locally as well: a superseded request must not clear the spinner or drop the live request's
+    // controller on its way out, or reset() would no longer be able to abort what is actually in flight.
+    const ownController = new AbortController()
+    controller.value = ownController
+
+    loading.value = true
+    error.value = null
+    try {
+      const fetcher = kind === 'variant' ? getVariantCsvNamespaces : getScoreSetCsvNamespaces
+      const entries = await fetcher(urn.value, ownController.signal)
+      if (controller.value !== ownController) return
+      namespaces.value = entries
+      loadedUrn.value = urn.value
+      // Open on the common case and let the user narrow from there. Reopening for the same record
+      // short-circuits above, so a previous selection survives rather than being reset.
+      selectDefaults()
+    } catch (e: unknown) {
+      // An aborted request is a superseded one, not a failure to report.
+      if (axios.isCancel(e) || controller.value !== ownController) return
+      namespaces.value = []
+      selected.value = []
+      selectedExtras.value = []
+      loadedUrn.value = null
+      error.value = 'Could not load the available download options.'
+    } finally {
+      if (controller.value === ownController) {
+        loading.value = false
+        controller.value = null
+      }
+    }
+  }
+
+  function reset(): void {
+    controller.value?.abort()
+    controller.value = null
+    namespaces.value = []
+    selected.value = []
+    selectedExtras.value = []
+    loadedUrn.value = null
+    error.value = null
+    loading.value = false
+  }
+
+  return {
+    namespaces,
+    sections,
+    hasNamespaces,
+    loading,
+    error,
+    selected,
+    selectedExtras,
+    formattingExtraOptions,
+    totalColumnGroups,
+    selectedColumnGroups,
+    allSelected,
+    selectionSummary,
+    selectAll,
+    selectDefaults,
+    toggleAll,
+    load,
+    reset
+  }
+}
diff --git a/src/composables/use-score-set-downloads.test.ts b/src/composables/use-score-set-downloads.test.ts
new file mode 100644
index 00000000..2c9639df
--- /dev/null
+++ b/src/composables/use-score-set-downloads.test.ts
@@ -0,0 +1,255 @@
+import {beforeEach, describe, expect, it, vi} from 'vitest'
+import {ref, watch, type Ref} from 'vue'
+
+import {useScoreSetDownloads} from './use-score-set-downloads'
+
+const downloadScoreSetFile = vi.fn()
+const downloadScoreSetVariantData = vi.fn()
+const downloadMappedVariants = vi.fn()
+
+vi.mock('@/api/mavedb', () => ({
+  downloadScoreSetFile: (...args: unknown[]) => downloadScoreSetFile(...args),
+  downloadScoreSetVariantData: (...args: unknown[]) => downloadScoreSetVariantData(...args),
+  downloadMappedVariants: (...args: unknown[]) => downloadMappedVariants(...args)
+}))
+
+// The real one reaches for `document`; these tests run in the node environment.
+vi.mock('@/lib/downloads', () => ({triggerDownload: vi.fn()}))
+
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+const SCORE_SET = ref({urn: 'urn:mavedb:00000001-a-1'} as any)
+
+/** Collect every value the progress ref takes; it is back to null by the time a download resolves. */
+function recordProgress(source: Ref<number | null>): {values: (number | null)[]; stop: () => void} {
+  const values: (number | null)[] = []
+  const stop = watch(source, (value) => values.push(value), {flush: 'sync'})
+  return {values, stop}
+}
+
+beforeEach(() => {
+  downloadScoreSetFile.mockReset()
+  downloadScoreSetVariantData.mockReset()
+  downloadMappedVariants.mockReset()
+})
+
+describe('useScoreSetDownloads download indicator', () => {
+  it('is idle before anything is requested', () => {
+    const {fileDownloadInProgress, fileDownloadLabel} = useScoreSetDownloads({scoreSet: SCORE_SET})
+
+    expect(fileDownloadInProgress.value).toBe(false)
+    expect(fileDownloadLabel.value).toBeNull()
+  })
+
+  it('names the file being prepared while the request is in flight', async () => {
+    let release: (csv: string) => void = () => {}
+    downloadScoreSetFile.mockReturnValueOnce(new Promise((resolve) => (release = resolve)))
+    const {downloadFile, fileDownloadInProgress, fileDownloadLabel} = useScoreSetDownloads({scoreSet: SCORE_SET})
+
+    const pending = downloadFile('counts')
+    expect(fileDownloadInProgress.value).toBe(true)
+    expect(fileDownloadLabel.value).toBe('Counts')
+
+    release('accession,c_0\n')
+    await pending
+
+    expect(fileDownloadInProgress.value).toBe(false)
+    expect(fileDownloadLabel.value).toBeNull()
+  })
+
+  it('leaves a CSV indeterminate, since a gzipped body has no measurable total', async () => {
+    let release: (csv: string) => void = () => {}
+    downloadScoreSetFile.mockReturnValueOnce(new Promise((resolve) => (release = resolve)))
+    const {downloadFile, fileDownloadProgress} = useScoreSetDownloads({scoreSet: SCORE_SET})
+
+    const pending = downloadFile('scores')
+    expect(fileDownloadProgress.value).toBeNull()
+
+    release('accession,score\n')
+    await pending
+  })
+
+  it('clears the indicator when the request fails', async () => {
+    // Otherwise a failed 10MB download leaves the buttons disabled behind a bar that never stops.
+    downloadScoreSetFile.mockRejectedValueOnce(new Error('boom'))
+    const {downloadFile, fileDownloadInProgress} = useScoreSetDownloads({scoreSet: SCORE_SET})
+
+    await expect(downloadFile('scores')).rejects.toThrow('boom')
+
+    expect(fileDownloadInProgress.value).toBe(false)
+  })
+
+  it('ignores a second request while one is already running', async () => {
+    let release: (csv: string) => void = () => {}
+    downloadScoreSetFile.mockReturnValueOnce(new Promise((resolve) => (release = resolve)))
+    const {downloadFile, fileDownloadLabel} = useScoreSetDownloads({scoreSet: SCORE_SET})
+
+    const pending = downloadFile('scores')
+    await downloadFile('counts')
+
+    // The first request still owns the indicator, and the second never reached the API.
+    expect(fileDownloadLabel.value).toBe('Scores')
+    expect(downloadScoreSetFile).toHaveBeenCalledTimes(1)
+
+    release('accession,score\n')
+    await pending
+  })
+
+  it('covers the custom-columns download too', async () => {
+    let release: (csv: string) => void = () => {}
+    downloadScoreSetVariantData.mockReturnValueOnce(new Promise((resolve) => (release = resolve)))
+    const {downloadMultipleData, fileDownloadLabel} = useScoreSetDownloads({scoreSet: SCORE_SET})
+
+    const pending = downloadMultipleData({namespaces: ['scores'], extras: []})
+    expect(fileDownloadLabel.value).toBe('Custom data')
+
+    release('accession,score\n')
+    await pending
+
+    expect(fileDownloadLabel.value).toBeNull()
+  })
+
+  it('covers the mapped-variants download too', async () => {
+    let release: (data: unknown) => void = () => {}
+    downloadMappedVariants.mockReturnValueOnce(new Promise((resolve) => (release = resolve)))
+    const {downloadMappedVariantsFile, fileDownloadLabel} = useScoreSetDownloads({scoreSet: SCORE_SET})
+
+    const pending = downloadMappedVariantsFile()
+    expect(fileDownloadLabel.value).toBe('Mapped variants')
+
+    release([])
+    await pending
+
+    expect(fileDownloadLabel.value).toBeNull()
+  })
+
+  it('does nothing without a score set', async () => {
+    const {downloadFile, fileDownloadInProgress} = useScoreSetDownloads({scoreSet: ref(null)})
+
+    await downloadFile('scores')
+
+    expect(downloadScoreSetFile).not.toHaveBeenCalled()
+    expect(fileDownloadInProgress.value).toBe(false)
+  })
+})
+
+describe('useScoreSetDownloads annotation streaming shares the indicator', () => {
+  /** Serve an NDJSON body in the given chunks, with an optional X-Total-Count. */
+  function mockStream(chunks: string[], totalCount: string | null = '4') {
+    const encoder = new TextEncoder()
+    let index = 0
+    vi.stubGlobal(
+      'fetch',
+      vi.fn().mockResolvedValue({
+        ok: true,
+        headers: {get: (name: string) => (name === 'X-Total-Count' ? totalCount : null)},
+        body: {
+          getReader: () => ({
+            read: async () =>
+              index < chunks.length ? {done: false, value: encoder.encode(chunks[index++])} : {done: true}
+          })
+        }
+      })
+    )
+  }
+
+  beforeEach(() => {
+    // The stream saves its file through Blob + an anchor click rather than `triggerDownload`, so the
+    // node environment needs both stubbed for the completion path to run.
+    vi.stubGlobal('Blob', class {})
+    vi.stubGlobal('URL', {createObjectURL: () => 'blob:stub', revokeObjectURL: () => {}})
+    vi.stubGlobal('document', {createElement: () => ({click: () => {}})})
+  })
+
+  it('reports a percentage, since a VA-Spec stream can count records', async () => {
+    mockStream(['{"a":1}\n', '{"a":2}\n'], '2')
+    const downloads = useScoreSetDownloads({scoreSet: SCORE_SET})
+    const {values, stop} = recordProgress(downloads.fileDownloadProgress)
+
+    const pending = downloads.streamVariantAnnotations('study-result', 'Functional Study Result')
+    expect(downloads.fileDownloadLabel.value).toBe('Functional Study Result')
+    await pending
+    stop()
+
+    // One record then both, then released.
+    expect(values).toEqual([50, 100, null])
+  })
+
+  it('refuses to save a truncated download', async () => {
+    // The bar stalling partway is the visible symptom of the server generator raising mid-stream: the 200
+    // and its headers are long gone, so a short body is all the client ever sees. Saving it would hand
+    // the user a silently incomplete file.
+    mockStream(['{"a":1}\n'], '5')
+    const downloads = useScoreSetDownloads({scoreSet: SCORE_SET})
+
+    await expect(downloads.streamVariantAnnotations('functional-statement')).rejects.toThrow('received 1 of 5 records')
+    expect(downloads.fileDownloadInProgress.value).toBe(false)
+  })
+
+  it('counts records by byte, so a multi-byte character cannot skew the total', async () => {
+    // The old implementation decoded each chunk to a string first; retaining bytes is both exact and what
+    // keeps a large download out of the tab's memory.
+    mockStream(['{"p":"p.Trp26€"}\n', '{"p":"p.Met1?"}\n'], '2')
+    const downloads = useScoreSetDownloads({scoreSet: SCORE_SET})
+    const {values, stop} = recordProgress(downloads.fileDownloadProgress)
+
+    await downloads.streamVariantAnnotations('study-result')
+    stop()
+
+    expect(values).toEqual([50, 100, null])
+  })
+
+  it('does not overshoot 100% across chunk boundaries', async () => {
+    // `split('\n').length` counted one extra per chunk, so a record split across chunks was double
+    // counted and the old bar sailed past 100%.
+    mockStream(['{"a":1}\n{"a":', '2}\n{"a":3}\n{"a":4}\n'], '4')
+    const downloads = useScoreSetDownloads({scoreSet: SCORE_SET})
+    const {values, stop} = recordProgress(downloads.fileDownloadProgress)
+
+    await downloads.streamVariantAnnotations('study-result')
+    stop()
+
+    expect(Math.max(...values.map((value) => value ?? 0))).toBe(100)
+  })
+
+  it('stays indeterminate when the total count header is absent', async () => {
+    // Previously this divided by zero and set the bar to Infinity.
+    mockStream(['{"a":1}\n'], null)
+    const downloads = useScoreSetDownloads({scoreSet: SCORE_SET})
+    const {values, stop} = recordProgress(downloads.fileDownloadProgress)
+
+    await downloads.streamVariantAnnotations('study-result')
+    stop()
+
+    expect(values.every((value) => value === null)).toBe(true)
+  })
+
+  it('blocks a CSV download while a stream is running, since they share one indicator', async () => {
+    let releaseRead: () => void = () => {}
+    const encoder = new TextEncoder()
+    vi.stubGlobal(
+      'fetch',
+      vi.fn().mockResolvedValue({
+        ok: true,
+        headers: {get: () => '1'},
+        body: {
+          getReader: () => ({
+            read: () =>
+              new Promise((resolve) => {
+                releaseRead = () => resolve({done: false, value: encoder.encode('{"a":1}\n')})
+              })
+          })
+        }
+      })
+    )
+    const {streamVariantAnnotations, downloadFile, fileDownloadLabel} = useScoreSetDownloads({scoreSet: SCORE_SET})
+
+    void streamVariantAnnotations('study-result', 'Functional Study Result')
+    await Promise.resolve()
+    await Promise.resolve()
+    await downloadFile('scores')
+
+    expect(fileDownloadLabel.value).toBe('Functional Study Result')
+    expect(downloadScoreSetFile).not.toHaveBeenCalled()
+    releaseRead()
+  })
+})
diff --git a/src/composables/use-score-set-downloads.ts b/src/composables/use-score-set-downloads.ts
index 44385d67..c0431ab9 100644
--- a/src/composables/use-score-set-downloads.ts
+++ b/src/composables/use-score-set-downloads.ts
@@ -1,5 +1,7 @@
 import {computed, ref, type Ref} from 'vue'
 
+import type {CsvExtraOption} from '@/composables/use-csv-namespaces'
+
 import {downloadScoreSetFile, downloadScoreSetVariantData, downloadMappedVariants} from '@/api/mavedb'
 import config from '@/config'
 import {triggerDownload} from '@/lib/downloads'
@@ -11,55 +13,75 @@ export const TEXT_COLUMNS = ['hgvs_nt', 'hgvs_splice', 'hgvs_pro']
 
 interface UseScoreSetDownloadsOptions {
   scoreSet: Ref<ScoreSet | null>
-  hasCounts?: Ref<boolean>
 }
 
-export function useScoreSetDownloads({scoreSet, hasCounts}: UseScoreSetDownloadsOptions) {
+export function useScoreSetDownloads({scoreSet}: UseScoreSetDownloadsOptions) {
   const customDialogVisible = ref(false)
-  const selectedDataOptions = ref<string[]>([])
-  const annotatedDownloadInProgress = ref(false)
-  const annotatedDownloadProgress = ref(0)
   const streamController = ref<AbortController | null>(null)
 
-  const dataTypeOptions = computed(() => {
-    const options = [
-      {label: 'Scores', value: 'scores'},
-      {label: 'Mapped HGVS', value: 'mappedHgvs'},
-      {label: 'Custom columns', value: 'includeCustomColumns'},
-      {label: 'Without NA columns', value: 'dropNaColumns'}
-    ]
-    if (hasCounts?.value) {
-      options.splice(1, 0, {label: 'Counts', value: 'counts'})
+  /** What file is currently being prepared, or null when idle. One indicator for every download here. */
+  const fileDownloadLabel = ref<string | null>(null)
+
+  /**
+   * Percent complete, or null when the download cannot report progress.
+   *
+   * Only the VA-Spec streams can: they carry `X-Total-Count` and emit one NDJSON record per line, so
+   * records can be tallied as they arrive. A CSV arrives as a single gzipped body whose `Content-Length`
+   * is the *compressed* size, which browsers compare against decompressed bytes received, so no usable
+   * percentage exists — and most of that wait is the server building the file before any byte is sent.
+   */
+  const fileDownloadProgress = ref<number | null>(null)
+
+  const fileDownloadInProgress = computed(() => fileDownloadLabel.value !== null)
+
+  /** Run *download* with the indicator showing, clearing it even if the request fails. */
+  async function withIndicator<T>(label: string, download: () => Promise<T>): Promise<T | undefined> {
+    if (fileDownloadLabel.value !== null) return
+    fileDownloadLabel.value = label
+    try {
+      return await download()
+    } finally {
+      fileDownloadLabel.value = null
+      fileDownloadProgress.value = null
     }
-    return options
-  })
+  }
+
+  /** Formatting flags. Column groups come from the csv-namespaces endpoint via MvCsvColumnDialog. */
+  const extraDownloadOptions: CsvExtraOption[] = [
+    {label: "Omit HGVS columns this score set doesn't use", value: 'dropUnusedHgvsColumns'}
+  ]
 
   async function downloadFile(type: 'scores' | 'counts') {
     if (!scoreSet.value) return
-    const data = await downloadScoreSetFile(scoreSet.value.urn, type)
-    triggerDownload(data, `${scoreSet.value.urn}_${type}.csv`)
+    await withIndicator(type === 'scores' ? 'Scores' : 'Counts', async () => {
+      const data = await downloadScoreSetFile(scoreSet.value!.urn, type)
+      triggerDownload(data, `${scoreSet.value!.urn}_${type}.csv`)
+    })
   }
 
-  async function downloadMultipleData() {
+  /**
+   * Download the score set's variant data with the chosen column groups. Namespaces pass through
+   * verbatim — they are the API's own vocabulary. (This previously sent an unsupported `data_type`
+   * parameter, so every selection was silently ignored.)
+   */
+  async function downloadMultipleData({namespaces, extras}: {namespaces: string[]; extras: string[]}) {
     if (!scoreSet.value) return
     const params = new URLSearchParams()
-    for (const opt of selectedDataOptions.value) {
-      if (opt === 'scores') params.append('data_type', 'scores')
-      else if (opt === 'counts') params.append('data_type', 'counts')
-      else if (opt === 'mappedHgvs') params.append('include_post_mapped_hgvs', 'true')
-      else if (opt === 'includeCustomColumns') params.append('include_custom_columns', 'true')
-      else if (opt === 'dropNaColumns') params.append('drop_na_columns', 'true')
-    }
-    if (!params.has('data_type')) params.append('data_type', 'scores')
-    const data = await downloadScoreSetVariantData(scoreSet.value.urn, params)
-    triggerDownload(data, `${scoreSet.value.urn}_custom.csv`)
-    customDialogVisible.value = false
+    for (const namespace of namespaces) params.append('namespaces', namespace)
+    if (extras.includes('dropUnusedHgvsColumns')) params.append('drop_unused_hgvs_columns', 'true')
+    await withIndicator('Custom data', async () => {
+      const data = await downloadScoreSetVariantData(scoreSet.value!.urn, params)
+      triggerDownload(data, `${scoreSet.value!.urn}_custom.csv`)
+      customDialogVisible.value = false
+    })
   }
 
   async function downloadMappedVariantsFile() {
     if (!scoreSet.value) return
-    const data = await downloadMappedVariants(scoreSet.value.urn)
-    triggerDownload(JSON.stringify(data), `${scoreSet.value.urn}_mapped_variants.json`, 'text/json')
+    await withIndicator('Mapped variants', async () => {
+      const data = await downloadMappedVariants(scoreSet.value!.urn)
+      triggerDownload(JSON.stringify(data), `${scoreSet.value!.urn}_mapped_variants.json`, 'text/json')
+    })
   }
 
   function downloadMetadata() {
@@ -71,22 +93,25 @@ export function useScoreSetDownloads({scoreSet, hasCounts}: UseScoreSetDownloads
   function abortStream() {
     if (streamController.value) {
       streamController.value.abort()
-      annotatedDownloadInProgress.value = false
-      annotatedDownloadProgress.value = 0
+      fileDownloadLabel.value = null
+      fileDownloadProgress.value = null
     }
   }
 
-  async function streamVariantAnnotations(annotationType: string) {
-    if (!scoreSet.value) return
-    abortStream()
+  async function streamVariantAnnotations(annotationType: string, label = 'annotations') {
+    const urn = scoreSet.value?.urn
+    if (!urn) return
+    await withIndicator(label, () => streamAnnotationsInto(urn, annotationType))
+  }
+
+  async function streamAnnotationsInto(urn: string, annotationType: string) {
     streamController.value = new AbortController()
 
     try {
-      annotatedDownloadInProgress.value = true
-      const response = await fetch(
-        `${config.apiBaseUrl}/score-sets/${scoreSet.value.urn}/annotated-variants/${annotationType}`,
-        {signal: streamController.value.signal, headers: {Accept: 'application/x-ndjson'}}
-      )
+      const response = await fetch(`${config.apiBaseUrl}/score-sets/${urn}/annotated-variants/${annotationType}`, {
+        signal: streamController.value.signal,
+        headers: {Accept: 'application/x-ndjson'}
+      })
 
       if (!response.ok) {
         throw new Error(`HTTP ${response.status}: ${response.statusText}`)
@@ -96,27 +121,45 @@ export function useScoreSetDownloads({scoreSet, hasCounts}: UseScoreSetDownloads
       const reader = response.body?.getReader()
       if (!reader) throw new Error('Response body is not readable')
 
-      const decoder = new TextDecoder()
-      const chunks: string[] = []
+      // Held as raw bytes rather than decoded strings. Accumulating strings and then joining them cost
+      // roughly five times the payload — JS strings are UTF-16, so the decoded chunks alone doubled it,
+      // the join doubled that again, and the Blob copied the result. A large pathogenicity download ran
+      // the tab out of memory.
+      const parts: Uint8Array[] = []
       let processedCount = 0
 
       while (true) {
         const {done, value} = await reader.read()
-        if (done) {
-          const blob = new Blob([chunks.join('')], {type: 'application/x-ndjson'})
-          const url = URL.createObjectURL(blob)
-          const anchor = document.createElement('a')
-          anchor.href = url
-          anchor.download = `${scoreSet.value!.urn}_annotated_variants_${annotationType}.ndjson`
-          anchor.click()
-          URL.revokeObjectURL(url)
-          break
+        if (done) break
+
+        parts.push(value)
+        // NDJSON terminates every record with a newline, and 0x0A cannot appear inside a multi-byte UTF-8
+        // sequence, so counting the byte is exact and needs no decoding or chunk-boundary bookkeeping.
+        for (const byte of value) {
+          if (byte === 0x0a) processedCount += 1
         }
-        const chunk = decoder.decode(value)
-        chunks.push(chunk)
-        processedCount += chunk.split('\n').length
-        annotatedDownloadProgress.value = Math.round((processedCount / totalCount) * 100)
+        // Without a total there is nothing to divide by; stay indeterminate rather than report Infinity.
+        fileDownloadProgress.value =
+          totalCount > 0 ? Math.min(100, Math.round((processedCount / totalCount) * 100)) : null
       }
+
+      // The server generator yields one line per variant, so a short body means it stopped early —
+      // status and headers went out with the first chunk, so a truncated stream is the only symptom it
+      // can produce. Refuse to save a file that is quietly missing records.
+      if (totalCount > 0 && processedCount < totalCount) {
+        throw new Error(
+          `Download incomplete: received ${processedCount} of ${totalCount} records.` +
+            ' The server stopped sending partway through; check the API logs.'
+        )
+      }
+
+      const blob = new Blob(parts as BlobPart[], {type: 'application/x-ndjson'})
+      const url = URL.createObjectURL(blob)
+      const anchor = document.createElement('a')
+      anchor.href = url
+      anchor.download = `${urn}_annotated_variants_${annotationType}.ndjson`
+      anchor.click()
+      URL.revokeObjectURL(url)
     } catch (error: unknown) {
       const message = error instanceof Error ? error.message : 'Unknown error'
       if (message !== 'The user aborted a request.') {
@@ -124,20 +167,17 @@ export function useScoreSetDownloads({scoreSet, hasCounts}: UseScoreSetDownloads
       }
     } finally {
       streamController.value = null
-      annotatedDownloadInProgress.value = false
-      annotatedDownloadProgress.value = 0
     }
   }
 
   return {
     // State
     customDialogVisible,
-    selectedDataOptions,
-    annotatedDownloadInProgress,
-    annotatedDownloadProgress,
+    fileDownloadInProgress,
+    fileDownloadLabel,
+    fileDownloadProgress,
 
-    // Computed
-    dataTypeOptions,
+    extraDownloadOptions,
 
     // Methods
     downloadFile,
diff --git a/src/composables/use-variant-lookup.ts b/src/composables/use-variant-lookup.ts
index f7b6bd57..5ffacf8f 100644
--- a/src/composables/use-variant-lookup.ts
+++ b/src/composables/use-variant-lookup.ts
@@ -1,7 +1,7 @@
-import axios from 'axios'
 import {computed, ref, shallowRef, watch, type ComputedRef, type Ref} from 'vue'
 
 import {
+  downloadVariantCsv,
   getVariantAnnotation,
   getVariantDetail,
   getHistogramVariantData,
@@ -17,6 +17,7 @@ import {
   getPrimaryCalibration
 } from '@/lib/calibrations'
 import {triggerDownload} from '@/lib/downloads'
+import {describeRequestError} from '@/lib/errors'
 import {getExperimentKeyword} from '@/lib/experiments'
 import {parseScoreSetVariantData, type Variant} from '@/lib/variants'
 import type {MeasurementType} from '@/lib/measurement-types'
@@ -84,6 +85,9 @@ export interface UseVariantLookupReturn {
 
   // Downloads
   fetchVariantAnnotations: (annotationType: string) => Promise<void>
+  downloadVariantCsvFile: (namespaces?: string[]) => Promise<void>
+  /** What download is in flight, or null when idle. Indeterminate; see use-score-set-downloads. */
+  downloadInProgressLabel: Ref<string | null>
 }
 
 /**
@@ -115,6 +119,7 @@ export function useVariantLookup(
   const variants = ref<VariantEntry[]>([])
   const variantsStatus = ref<'NotLoaded' | 'Loading' | 'Loaded' | 'Error'>('NotLoaded')
   const selectedVariantUrn = ref<string | null>(null)
+  const downloadInProgressLabel = ref<string | null>(null)
   const showNucleotide = ref(true)
   const showProtein = ref(true)
   const showAssociatedNucleotide = ref(true)
@@ -284,27 +289,45 @@ export function useVariantLookup(
 
   async function fetchVariantAnnotations(annotationType: string) {
     const activeVariant = selectedVariantDetail.value
-    if (!activeVariant?.urn) return
+    if (!activeVariant?.urn || downloadInProgressLabel.value !== null) return
 
+    downloadInProgressLabel.value = 'annotations'
     try {
       const data = await getVariantAnnotation(activeVariant.urn, annotationType)
       triggerDownload(JSON.stringify(data), activeVariant.urn + '_' + annotationType + '.json', 'text/json')
     } catch (error: unknown) {
-      let serverMessage = ''
-      if (axios.isAxiosError(error) && error.response?.data) {
-        const data = error.response.data
-        if (typeof data === 'string') serverMessage = data
-        else if (typeof data === 'object' && data !== null && 'detail' in data) serverMessage = String(data.detail)
-        else serverMessage = JSON.stringify(data)
-      } else {
-        serverMessage = error instanceof Error ? error.message : 'Unknown error.'
-      }
       options?.toast?.add({
         severity: 'error',
         summary: 'Download failed',
-        detail: `Could not fetch variant annotation: ${serverMessage}`,
+        detail: `Could not fetch variant annotation: ${describeRequestError(error)}`,
+        life: 4000
+      })
+    } finally {
+      downloadInProgressLabel.value = null
+    }
+  }
+
+  /**
+   * Download the selected measurement's clinical CSV — the flat counterpart to
+   * `fetchVariantAnnotations`. Omitting `namespaces` asks the server for its default set.
+   */
+  async function downloadVariantCsvFile(namespaces?: string[]) {
+    const activeVariant = selectedVariantDetail.value
+    if (!activeVariant?.urn || downloadInProgressLabel.value !== null) return
+
+    downloadInProgressLabel.value = 'variant CSV'
+    try {
+      const data = await downloadVariantCsv(activeVariant.urn, namespaces)
+      triggerDownload(data, `${activeVariant.urn}.csv`, 'text/csv')
+    } catch (error: unknown) {
+      options?.toast?.add({
+        severity: 'error',
+        summary: 'Download failed',
+        detail: `Could not download the variant table: ${describeRequestError(error)}`,
         life: 4000
       })
+    } finally {
+      downloadInProgressLabel.value = null
     }
   }
 
@@ -414,6 +437,8 @@ export function useVariantLookup(
     getKeyword,
     geneName,
     uniqueAssayCount,
-    fetchVariantAnnotations
+    fetchVariantAnnotations,
+    downloadVariantCsvFile,
+    downloadInProgressLabel
   }
 }
diff --git a/src/lib/errors.test.ts b/src/lib/errors.test.ts
new file mode 100644
index 00000000..e258023a
--- /dev/null
+++ b/src/lib/errors.test.ts
@@ -0,0 +1,65 @@
+import {describe, expect, it, vi} from 'vitest'
+
+import {describeRequestError, getErrorResponse} from './errors'
+
+vi.mock('axios', () => {
+  const isAxiosError = (error: unknown) => Boolean((error as {isAxiosError?: boolean})?.isAxiosError)
+  return {default: {isAxiosError}, isAxiosError}
+})
+
+function axiosError(data: unknown): unknown {
+  return {isAxiosError: true, response: {status: 400, data}, message: 'Request failed'}
+}
+
+describe('describeRequestError', () => {
+  it('prefers a string detail from the server', () => {
+    expect(describeRequestError(axiosError({detail: 'Score set is private.'}))).toBe('Score set is private.')
+  })
+
+  it('serializes a non-string detail rather than losing it', () => {
+    const detail = [{loc: ['query', 'namespaces', 0], msg: 'Value error, must be one of ...'}]
+
+    const message = describeRequestError(axiosError({detail}))
+
+    expect(message).toContain('namespaces')
+    expect(message).toContain('Value error')
+  })
+
+  it('returns a plain string body as-is', () => {
+    expect(describeRequestError(axiosError('Gateway timeout'))).toBe('Gateway timeout')
+  })
+
+  it('serializes a response body with no detail field', () => {
+    expect(describeRequestError(axiosError({error: 'nope'}))).toBe('{"error":"nope"}')
+  })
+
+  it('falls back to the exception message for non-request failures', () => {
+    expect(describeRequestError(new Error('Network down'))).toBe('Network down')
+  })
+
+  it('falls back to the exception message when there is no response body', () => {
+    expect(describeRequestError({isAxiosError: true, message: 'Request failed'})).toBe('Unknown error.')
+  })
+
+  it('always returns something renderable', () => {
+    expect(describeRequestError(undefined)).toBe('Unknown error.')
+    expect(describeRequestError('a bare string')).toBe('Unknown error.')
+  })
+})
+
+describe('getErrorResponse', () => {
+  it('extracts the status and body from an Axios error', () => {
+    expect(getErrorResponse(axiosError({detail: 'Score set is private.'}))).toEqual({
+      status: 400,
+      data: {detail: 'Score set is private.'}
+    })
+  })
+
+  it('falls back to a 500 for non-Axios errors', () => {
+    expect(getErrorResponse(new Error('Network down'))).toEqual({status: 500})
+  })
+
+  it('falls back to a 500 when the Axios error has no response', () => {
+    expect(getErrorResponse({isAxiosError: true, message: 'Request failed'})).toEqual({status: 500})
+  })
+})
diff --git a/src/lib/errors.ts b/src/lib/errors.ts
new file mode 100644
index 00000000..db0f50e1
--- /dev/null
+++ b/src/lib/errors.ts
@@ -0,0 +1,43 @@
+import axios, {isAxiosError} from 'axios'
+
+/**
+ * Extract a message worth showing a user from a failed request.
+ *
+ * Prefers the server's own `detail`, which is where FastAPI puts the human-readable reason, and falls
+ * back through the raw response body to the exception message. Always returns something renderable, so
+ * callers can drop it straight into a toast.
+ *
+ * For the status code rather than the message, see `getErrorResponse` in `@/api/mavedb`.
+ */
+export function describeRequestError(error: unknown): string {
+  if (axios.isAxiosError(error) && error.response?.data) {
+    const data = error.response.data
+    if (typeof data === 'string') return data
+    if (typeof data === 'object' && data !== null && 'detail' in data) {
+      const detail = (data as {detail: unknown}).detail
+      // A string detail is the common case. A validation error is an array of objects; JSON is more use
+      // to a reader than "AxiosError: Request failed with status code 422".
+      return typeof detail === 'string' ? detail : JSON.stringify(detail)
+    }
+    return JSON.stringify(data)
+  }
+  return error instanceof Error ? error.message : 'Unknown error.'
+}
+
+export interface ErrorResponse {
+  status: number
+  data?: Record<string, unknown>
+}
+
+/**
+ * Extract a normalized status and body from a caught Axios error.
+ *
+ * The counterpart to `describeRequestError`: use this when the caller branches on the status code, and
+ * that one when it just needs something to show the user.
+ */
+export function getErrorResponse(e: unknown): ErrorResponse {
+  if (isAxiosError(e) && e.response) {
+    return {status: e.response.status, data: e.response.data as Record<string, unknown>}
+  }
+  return {status: 500}
+}
diff --git a/src/lib/genes.ts b/src/lib/genes.ts
index 4b711a76..88d7d4aa 100644
--- a/src/lib/genes.ts
+++ b/src/lib/genes.ts
@@ -1,4 +1,5 @@
-import {getErrorResponse, type GeneResponse, type GeneScoreSet} from '@/api/mavedb'
+import {type GeneResponse, type GeneScoreSet} from '@/api/mavedb'
+import {getErrorResponse} from '@/lib/errors'
 
 export type GeneErrorState = 'not-found' | 'retryable'
 
diff --git a/src/lib/orcid.ts b/src/lib/orcid.ts
index 615ac72c..15405599 100644
--- a/src/lib/orcid.ts
+++ b/src/lib/orcid.ts
@@ -33,7 +33,7 @@ import {v4 as uuidv4} from 'uuid'
 import {computed, ref, Ref} from 'vue'
 
 import config from '../config'
-import {getErrorResponse} from '@/api/mavedb'
+import {getErrorResponse} from '@/lib/errors'
 
 export interface OidcUserProfileBase {
   auth_time: number
diff --git a/src/schema/openapi.d.ts b/src/schema/openapi.d.ts
index d07f1dbc..a745ac0e 100644
--- a/src/schema/openapi.d.ts
+++ b/src/schema/openapi.d.ts
@@ -747,6 +747,32 @@ export interface paths {
      */
     delete: operations["delete_score_set_api_v1_score_sets__urn__delete"];
   };
+  "/api/v1/score-sets/{urn}/csv-namespaces": {
+    /**
+     * List the CSV column namespaces this score set has data for
+     * @description List the CSV column namespaces this score set has data for, labeled and grouped for a picker.
+     *
+     * Each entry's `namespace` is a value accepted by the `namespaces` parameter of the CSV endpoints.
+     * Deliberately a separate request rather than a field on the score set: it costs several queries and is
+     * only needed when a user opens a download dialog, so it should not sit on the score-set page's
+     * critical path.
+     *
+     * Parameters
+     * __________
+     * urn : str
+     *     The URN of the score set to inspect.
+     * db : Session
+     *     The database session to use.
+     * user_data : Optional[UserData]
+     *     The user data of the current user. If None, no user-specific permissions are checked.
+     *
+     * Returns
+     * _______
+     * list[AvailableCsvNamespace]
+     *     The namespaces with data, each with a human-readable label and group.
+     */
+    get: operations["get_score_set_csv_namespaces_api_v1_score_sets__urn__csv_namespaces_get"];
+  };
   "/api/v1/score-sets/{urn}/variants/data": {
     /**
      * Get score set variant data in CSV format
@@ -765,11 +791,19 @@ export interface paths {
      *     The maximum number of variants to return. If None, returns all variants.
      * namespaces: List[str]
      *     The namespaces of all columns except for accession, hgvs_nt, hgvs_pro, and hgvs_splice.
-     *     Supported values: "scores", "counts", "vep", "gnomad", "clingen", and ClinVar-versioned
-     *     namespaces of the form "clinvar.YEAR_MONTH" (e.g. "clinvar.2024_01" for January 2024).
-     *     Multiple ClinVar namespaces with different YEAR_MONTH values may be requested simultaneously.
+     *     Supported values: "scores" (the required score column), "scores_custom" (the investigator's
+     *     remaining score columns, emitted under the "scores" prefix), "counts", "mavedb", "vep", "gnomad",
+     *     "clingen", "score_set", and ClinVar- and calibration-parameterized namespaces. Multiple ClinVar
+     *     and calibration namespaces may be requested simultaneously.
+     * drop_unused_hgvs_columns : bool, optional
+     *     Whether to omit the HGVS coordinate columns this score set does not use, e.g. hgvs_nt for a
+     *     protein-only score set. Defaults to False.
      * drop_na_columns : bool, optional
-     *     Whether to drop columns that contain only NA values. Defaults to False.
+     *     Deprecated spelling of drop_unused_hgvs_columns, accepted for one release.
+     * include_post_mapped_hgvs : bool, optional
+     *     Deprecated: equivalent to requesting the "mavedb" namespace. Accepted for one release.
+     * include_custom_columns : bool, optional
+     *     Deprecated: equivalent to requesting the "scores_custom" namespace. Accepted for one release.
      * db : Session
      *     The database session to use.
      * user_data : Optional[UserData]
@@ -1328,6 +1362,62 @@ export interface paths {
      */
     get: operations["get_variant_api_v1_variants__urn__get"];
   };
+  "/api/v1/variants/{urn}/csv-namespaces": {
+    /**
+     * List the CSV column namespaces this variant has data for
+     * @description List the CSV column namespaces this variant has data for, labeled and grouped for a picker.
+     *
+     * Widens over the variant's equivalent measurements the same way the CSV does, so a calibration
+     * belonging to another score set that also measured this allele is offered here too.
+     *
+     * Parameters
+     * __________
+     * urn : str
+     *     The URN of the variant to inspect.
+     * db : Session
+     *     The database session to use.
+     * user_data : Optional[UserData]
+     *     The user data of the current user. If None, no user-specific permissions are checked.
+     *
+     * Returns
+     * _______
+     * list[AvailableCsvNamespace]
+     *     The namespaces with data, each with a human-readable label and group.
+     */
+    get: operations["get_variant_csv_namespaces_api_v1_variants__urn__csv_namespaces_get"];
+  };
+  "/api/v1/variants/{urn}/csv": {
+    /**
+     * Get variant data in CSV format
+     * @description Return tabular data for a single variant, identified by URN, in CSV format.
+     *
+     * Where the variant-level annotation endpoints return nested VA-Spec objects, this flattens the same
+     * interpretation into columns a clinical information system can consume: ACMG criteria, evidence
+     * strengths, and evidence outcome codes alongside the measurement they were derived from.
+     *
+     * A row is emitted for every current measurement of the variant's ClinGen allele, so a variant assayed
+     * in several score sets yields several rows. The requested variant is always first.
+     *
+     * Parameters
+     * __________
+     * urn : str
+     *     The URN of the variant to fetch.
+     * namespaces : Optional[List[str]]
+     *     The groups of columns to include. When omitted, the response includes the fixed groups plus one
+     *     namespace per calibration eligible to annotate these measurements and the most recent ClinVar
+     *     release covering them.
+     * db : Session
+     *     The database session to use.
+     * user_data : Optional[UserData]
+     *     The user data of the current user. If None, no user-specific permissions are checked.
+     *
+     * Returns
+     * _______
+     * Any
+     *     StreamingResponse containing the CSV data.
+     */
+    get: operations["get_variant_csv_data_api_v1_variants__urn__csv_get"];
+  };
   "/api/v1/alphafold-files/version": {
     /**
      * Proxy Alphafold Index
@@ -1628,6 +1718,28 @@ export interface components {
       /** Version */
       version: string;
     };
+    /**
+     * AvailableCsvNamespace
+     * @description One CSV column namespace a record has data for, ready to be offered as a choice.
+     *
+     * Labels are served rather than derived client-side: only the server knows a calibration's title or a
+     * ClinVar release date.
+     */
+    AvailableCsvNamespace: {
+      /** Recordtype */
+      recordType?: string;
+      /** Namespace */
+      namespace: string;
+      /** Label */
+      label: string;
+      group: components["schemas"]["CsvNamespaceGroup"];
+      scoreSet?: components["schemas"]["ShorterScoreSet"] | null;
+      /**
+       * Selectedbydefault
+       * @default true
+       */
+      selectedByDefault?: boolean;
+    };
     /** Body_create_score_calibration_route_api_v1_score_calibrations__post */
     Body_create_score_calibration_route_api_v1_score_calibrations__post: {
       /**
@@ -2391,6 +2503,12 @@ export interface components {
        */
       copies: components["schemas"]["Range"] | number;
     };
+    /**
+     * CsvNamespaceGroup
+     * @description Presentational grouping, so a client can section a namespace picker.
+     * @enum {string}
+     */
+    CsvNamespaceGroup: "data" | "annotation" | "calibration" | "provenance";
     /**
      * CurrentUser
      * @description User view model for information about the current user.
@@ -5132,10 +5250,15 @@ export interface components {
       /** Uniprotidfrommappedmetadata */
       uniprotIdFromMappedMetadata?: string | null;
     };
-    /** ShorterScoreSet */
+    /**
+     * ShorterScoreSet
+     * @description A score set's identity: enough to name it in a UI without rooting the display on its URN.
+     */
     ShorterScoreSet: {
       /** Urn */
       urn: string;
+      /** Title */
+      title: string;
       /** Recordtype */
       recordType?: string;
     };
@@ -10128,6 +10251,69 @@ export interface operations {
       };
     };
   };
+  /**
+   * List the CSV column namespaces this score set has data for
+   * @description List the CSV column namespaces this score set has data for, labeled and grouped for a picker.
+   *
+   * Each entry's `namespace` is a value accepted by the `namespaces` parameter of the CSV endpoints.
+   * Deliberately a separate request rather than a field on the score set: it costs several queries and is
+   * only needed when a user opens a download dialog, so it should not sit on the score-set page's
+   * critical path.
+   *
+   * Parameters
+   * __________
+   * urn : str
+   *     The URN of the score set to inspect.
+   * db : Session
+   *     The database session to use.
+   * user_data : Optional[UserData]
+   *     The user data of the current user. If None, no user-specific permissions are checked.
+   *
+   * Returns
+   * _______
+   * list[AvailableCsvNamespace]
+   *     The namespaces with data, each with a human-readable label and group.
+   */
+  get_score_set_csv_namespaces_api_v1_score_sets__urn__csv_namespaces_get: {
+    parameters: {
+      header?: {
+        "x-active-roles"?: string | null;
+      };
+      path: {
+        urn: string;
+      };
+    };
+    responses: {
+      /** @description Successful Response */
+      200: {
+        content: {
+          "application/json": components["schemas"]["AvailableCsvNamespace"][];
+        };
+      };
+      /** @description Authentication required. */
+      401: {
+        content: never;
+      };
+      /** @description Forbidden. Insufficient permissions. */
+      403: {
+        content: never;
+      };
+      /** @description Resource not found. */
+      404: {
+        content: never;
+      };
+      /** @description Validation Error */
+      422: {
+        content: {
+          "application/json": components["schemas"]["HTTPValidationError"];
+        };
+      };
+      /** @description Internal server error. */
+      500: {
+        content: never;
+      };
+    };
+  };
   /**
    * Get score set variant data in CSV format
    * @description Return tabular variant data from a score set, identified by URN, in CSV format.
@@ -10145,11 +10331,19 @@ export interface operations {
    *     The maximum number of variants to return. If None, returns all variants.
    * namespaces: List[str]
    *     The namespaces of all columns except for accession, hgvs_nt, hgvs_pro, and hgvs_splice.
-   *     Supported values: "scores", "counts", "vep", "gnomad", "clingen", and ClinVar-versioned
-   *     namespaces of the form "clinvar.YEAR_MONTH" (e.g. "clinvar.2024_01" for January 2024).
-   *     Multiple ClinVar namespaces with different YEAR_MONTH values may be requested simultaneously.
+   *     Supported values: "scores" (the required score column), "scores_custom" (the investigator's
+   *     remaining score columns, emitted under the "scores" prefix), "counts", "mavedb", "vep", "gnomad",
+   *     "clingen", "score_set", and ClinVar- and calibration-parameterized namespaces. Multiple ClinVar
+   *     and calibration namespaces may be requested simultaneously.
+   * drop_unused_hgvs_columns : bool, optional
+   *     Whether to omit the HGVS coordinate columns this score set does not use, e.g. hgvs_nt for a
+   *     protein-only score set. Defaults to False.
    * drop_na_columns : bool, optional
-   *     Whether to drop columns that contain only NA values. Defaults to False.
+   *     Deprecated spelling of drop_unused_hgvs_columns, accepted for one release.
+   * include_post_mapped_hgvs : bool, optional
+   *     Deprecated: equivalent to requesting the "mavedb" namespace. Accepted for one release.
+   * include_custom_columns : bool, optional
+   *     Deprecated: equivalent to requesting the "scores_custom" namespace. Accepted for one release.
    * db : Session
    *     The database session to use.
    * user_data : Optional[UserData]
@@ -10167,11 +10361,24 @@ export interface operations {
         start?: number;
         /** @description Maximum number of variants to return */
         limit?: number;
-        /** @description One or more data types to include: "scores", "counts", "vep", "gnomad", "clingen", and/or ClinVar-versioned namespaces of the form "clinvar.YEAR_MONTH" (e.g. "clinvar.2024_01" for January 2024). */
+        /** @description One or more groups of columns to include. Naming any group replaces the default set rather than adding to it, so list every group you want. Fixed groups: "scores", "scores_custom", "counts", "mavedb", "vep", "gnomad", "clingen", "score_set", "relationship". Versioned groups: "clinvar.YEAR_MONTH" (e.g. "clinvar.2024_01") for one ClinVar release, and "calibration.<calibration urn>" for one score calibration's functional and ACMG interpretation. Several ClinVar and calibration namespaces may be requested at once; each carries its release or URN in the column header. To discover which namespaces are available for a record, query the `csv-namespaces` endpoint. */
         namespaces?: string[];
+        drop_unused_hgvs_columns?: boolean | null;
+        /**
+         * @deprecated
+         * @description Deprecated: use `drop_unused_hgvs_columns`, which names what it actually does. This parameter only ever dropped the HGVS coordinate columns a score set does not use, never every NA column. It will be removed in a future release; `drop_unused_hgvs_columns` wins if both are given.
+         */
         drop_na_columns?: boolean | null;
-        include_custom_columns?: boolean | null;
+        /**
+         * @deprecated
+         * @description Deprecated: request the `mavedb` namespace instead, e.g. `?namespaces=scores&namespaces=mavedb`. Passing true here is equivalent to appending that namespace. It will be removed in a future release.
+         */
         include_post_mapped_hgvs?: boolean | null;
+        /**
+         * @deprecated
+         * @description Deprecated: request the `scores_custom` namespace instead. Passing true here is equivalent to appending that namespace, whose columns are emitted under the `scores` prefix as before. It will be removed in a future release.
+         */
+        include_custom_columns?: boolean | null;
       };
       header?: {
         "x-active-roles"?: string | null;
@@ -10287,6 +10494,11 @@ export interface operations {
         start?: number;
         /** @description Number of variants to return */
         limit?: number;
+        drop_unused_hgvs_columns?: boolean | null;
+        /**
+         * @deprecated
+         * @description Deprecated: use `drop_unused_hgvs_columns`, which names what it actually does. This parameter only ever dropped the HGVS coordinate columns a score set does not use, never every NA column. It will be removed in a future release; `drop_unused_hgvs_columns` wins if both are given.
+         */
         drop_na_columns?: boolean | null;
       };
       header?: {
@@ -10348,6 +10560,11 @@ export interface operations {
         start?: number;
         /** @description Number of variants to return */
         limit?: number;
+        drop_unused_hgvs_columns?: boolean | null;
+        /**
+         * @deprecated
+         * @description Deprecated: use `drop_unused_hgvs_columns`, which names what it actually does. This parameter only ever dropped the HGVS coordinate columns a score set does not use, never every NA column. It will be removed in a future release; `drop_unused_hgvs_columns` wins if both are given.
+         */
         drop_na_columns?: boolean | null;
       };
       header?: {
@@ -12467,6 +12684,145 @@ export interface operations {
       };
     };
   };
+  /**
+   * List the CSV column namespaces this variant has data for
+   * @description List the CSV column namespaces this variant has data for, labeled and grouped for a picker.
+   *
+   * Widens over the variant's equivalent measurements the same way the CSV does, so a calibration
+   * belonging to another score set that also measured this allele is offered here too.
+   *
+   * Parameters
+   * __________
+   * urn : str
+   *     The URN of the variant to inspect.
+   * db : Session
+   *     The database session to use.
+   * user_data : Optional[UserData]
+   *     The user data of the current user. If None, no user-specific permissions are checked.
+   *
+   * Returns
+   * _______
+   * list[AvailableCsvNamespace]
+   *     The namespaces with data, each with a human-readable label and group.
+   */
+  get_variant_csv_namespaces_api_v1_variants__urn__csv_namespaces_get: {
+    parameters: {
+      header?: {
+        "x-active-roles"?: string | null;
+      };
+      path: {
+        urn: string;
+      };
+    };
+    responses: {
+      /** @description Successful Response */
+      200: {
+        content: {
+          "application/json": components["schemas"]["AvailableCsvNamespace"][];
+        };
+      };
+      /** @description Authentication required. */
+      401: {
+        content: never;
+      };
+      /** @description Forbidden. Insufficient permissions. */
+      403: {
+        content: never;
+      };
+      /** @description Resource not found. */
+      404: {
+        content: never;
+      };
+      /** @description Validation Error */
+      422: {
+        content: {
+          "application/json": components["schemas"]["HTTPValidationError"];
+        };
+      };
+      /** @description Internal server error. */
+      500: {
+        content: never;
+      };
+    };
+  };
+  /**
+   * Get variant data in CSV format
+   * @description Return tabular data for a single variant, identified by URN, in CSV format.
+   *
+   * Where the variant-level annotation endpoints return nested VA-Spec objects, this flattens the same
+   * interpretation into columns a clinical information system can consume: ACMG criteria, evidence
+   * strengths, and evidence outcome codes alongside the measurement they were derived from.
+   *
+   * A row is emitted for every current measurement of the variant's ClinGen allele, so a variant assayed
+   * in several score sets yields several rows. The requested variant is always first.
+   *
+   * Parameters
+   * __________
+   * urn : str
+   *     The URN of the variant to fetch.
+   * namespaces : Optional[List[str]]
+   *     The groups of columns to include. When omitted, the response includes the fixed groups plus one
+   *     namespace per calibration eligible to annotate these measurements and the most recent ClinVar
+   *     release covering them.
+   * db : Session
+   *     The database session to use.
+   * user_data : Optional[UserData]
+   *     The user data of the current user. If None, no user-specific permissions are checked.
+   *
+   * Returns
+   * _______
+   * Any
+   *     StreamingResponse containing the CSV data.
+   */
+  get_variant_csv_data_api_v1_variants__urn__csv_get: {
+    parameters: {
+      query?: {
+        /** @description One or more groups of columns to include. Naming any group replaces the default set rather than adding to it, so list every group you want. Fixed groups: "scores", "scores_custom", "counts", "mavedb", "vep", "gnomad", "clingen", "score_set", "relationship". Versioned groups: "clinvar.YEAR_MONTH" (e.g. "clinvar.2024_01") for one ClinVar release, and "calibration.<calibration urn>" for one score calibration's functional and ACMG interpretation. Several ClinVar and calibration namespaces may be requested at once; each carries its release or URN in the column header. To discover which namespaces are available for a record, query the `csv-namespaces` endpoint. */
+        namespaces?: string[] | null;
+      };
+      header?: {
+        "x-active-roles"?: string | null;
+      };
+      path: {
+        urn: string;
+      };
+    };
+    responses: {
+      /** @description Variant data in CSV format, one row per measurement of the variant's allele. Columns cover identity, mapped coordinates, the measured score, external annotations, and each requested calibration's functional and ACMG interpretation. */
+      200: {
+        content: {
+          "application/json": unknown;
+          "text/csv": unknown;
+        };
+      };
+      /** @description Bad request. Check parameters and payload. */
+      400: {
+        content: never;
+      };
+      /** @description Authentication required. */
+      401: {
+        content: never;
+      };
+      /** @description Forbidden. Insufficient permissions. */
+      403: {
+        content: never;
+      };
+      /** @description Resource not found. */
+      404: {
+        content: never;
+      };
+      /** @description Validation Error */
+      422: {
+        content: {
+          "application/json": components["schemas"]["HTTPValidationError"];
+        };
+      };
+      /** @description Internal server error. */
+      500: {
+        content: never;
+      };
+    };
+  };
   /**
    * Proxy Alphafold Index
    * @description Proxy the AlphaFold files index (XML document).