diff --git a/.github/actions/prune-repository/prune_test.py b/.github/actions/prune-repository/prune_test.py
index 5147d556bcb..fa07b4fb326 100644
--- a/.github/actions/prune-repository/prune_test.py
+++ b/.github/actions/prune-repository/prune_test.py
@@ -58,10 +58,10 @@ def test_sibling_or_website_job_does_not_add_brunch_extras(self) -> None:
         self.assertEqual(extra_paths_for_requested({TRANSPORT}), [])
         self.assertEqual(extra_paths_for_requested({WEBSITE}), [])
 
-    def test_transitive_core_in_the_closure_does_not_add_the_app(self) -> None:
+    def test_core_in_the_dependency_closure_does_not_add_the_app(self) -> None:
         dependencies = {
-            WEBSITE: frozenset({TRANSPORT}),
-            TRANSPORT: frozenset({CORE}),
+            WEBSITE: frozenset({CORE, TRANSPORT}),
+            TRANSPORT: frozenset(),
             CORE: frozenset(),
         }
         expanded = fixpoint_expand({WEBSITE}, dependencies)
diff --git a/.yarnrc.yml b/.yarnrc.yml
index 51acfada9eb..75546ed9dc5 100644
--- a/.yarnrc.yml
+++ b/.yarnrc.yml
@@ -2,6 +2,8 @@ approvedGitRepositories: []
 
 defaultSemverRangePrefix: ""
 
+enableConstraintsChecks: true
+
 enableScripts: false
 
 enableTransparentWorkspaces: false
diff --git a/apps/petrinaut-website/package.json b/apps/petrinaut-website/package.json
index 06d57bb1b91..f8e33266dd9 100644
--- a/apps/petrinaut-website/package.json
+++ b/apps/petrinaut-website/package.json
@@ -19,6 +19,7 @@
   },
   "dependencies": {
     "@ai-sdk/openai": "3.0.63",
+    "@hashintel/brunch-agent": "workspace:*",
     "@hashintel/brunch-agent-transport-aisdk": "workspace:*",
     "@hashintel/ds-components": "workspace:*",
     "@hashintel/ds-helpers": "workspace:*",
diff --git a/apps/petrinaut-website/src/main/app/local-storage-demo/brunch-ask-interactive-tool.tsx b/apps/petrinaut-website/src/main/app/local-storage-demo/brunch-ask-interactive-tool.tsx
index 1e8bed24fc6..7c4d01b4442 100644
--- a/apps/petrinaut-website/src/main/app/local-storage-demo/brunch-ask-interactive-tool.tsx
+++ b/apps/petrinaut-website/src/main/app/local-storage-demo/brunch-ask-interactive-tool.tsx
@@ -6,7 +6,7 @@ import {
   type BrunchAskOutput,
   parseBrunchAskInput,
   parseBrunchAskOutput,
-} from "@hashintel/brunch-agent-transport-aisdk/client-tools";
+} from "@hashintel/brunch-agent/client-tools";
 import { css } from "@hashintel/ds-helpers/css";
 import {
   definePetrinautAiInteractiveTool,
diff --git a/apps/petrinaut-website/src/main/app/local-storage-demo/brunch-ask-mapping.ts b/apps/petrinaut-website/src/main/app/local-storage-demo/brunch-ask-mapping.ts
index 833f3243c3a..a3887e6d9c4 100644
--- a/apps/petrinaut-website/src/main/app/local-storage-demo/brunch-ask-mapping.ts
+++ b/apps/petrinaut-website/src/main/app/local-storage-demo/brunch-ask-mapping.ts
@@ -1,7 +1,7 @@
 import type {
   BrunchAskInput,
   BrunchAskOutput,
-} from "@hashintel/brunch-agent-transport-aisdk/client-tools";
+} from "@hashintel/brunch-agent/client-tools";
 
 export const brunchAskFromComposerText = ({
   text,
diff --git a/apps/petrinaut-website/src/main/app/local-storage-demo/brunch-panel-transport.ts b/apps/petrinaut-website/src/main/app/local-storage-demo/brunch-panel-transport.ts
index 6069ee67f2a..3cdc3e19459 100644
--- a/apps/petrinaut-website/src/main/app/local-storage-demo/brunch-panel-transport.ts
+++ b/apps/petrinaut-website/src/main/app/local-storage-demo/brunch-panel-transport.ts
@@ -1,4 +1,4 @@
-import { SWEEP_TOOL_NAME } from "@hashintel/brunch-agent-transport-aisdk/client-tools";
+import { SWEEP_TOOL_NAME } from "@hashintel/brunch-agent/client-tools";
 
 import { sweepOutputSchema } from "../brunch-sweep-output";
 
diff --git a/apps/petrinaut-website/src/main/app/voice-interview/canonical-speech.test.ts b/apps/petrinaut-website/src/main/app/voice-interview/canonical-speech.test.ts
index 9e6b1c3d80f..dc12cda21c6 100644
--- a/apps/petrinaut-website/src/main/app/voice-interview/canonical-speech.test.ts
+++ b/apps/petrinaut-website/src/main/app/voice-interview/canonical-speech.test.ts
@@ -1,6 +1,6 @@
 import { describe, expect, test } from "vitest";
 
-import { ASK_TOOL_NAME } from "@hashintel/brunch-agent-transport-aisdk/client-tools";
+import { ASK_TOOL_NAME } from "@hashintel/brunch-agent/client-tools";
 
 import {
   hashCanonicalSpeechText,
diff --git a/apps/petrinaut-website/src/main/app/voice-interview/canonical-speech.ts b/apps/petrinaut-website/src/main/app/voice-interview/canonical-speech.ts
index 151db772ab5..bb111385b7e 100644
--- a/apps/petrinaut-website/src/main/app/voice-interview/canonical-speech.ts
+++ b/apps/petrinaut-website/src/main/app/voice-interview/canonical-speech.ts
@@ -1,7 +1,7 @@
 import {
   ASK_TOOL_NAME,
   parseBrunchAskInput,
-} from "@hashintel/brunch-agent-transport-aisdk/client-tools";
+} from "@hashintel/brunch-agent/client-tools";
 
 import { hashCanonicalSpeechText } from "../../../canonical-speech-fingerprint";
 
diff --git a/apps/petrinaut-website/src/main/app/voice-interview/interview-coverage.test.ts b/apps/petrinaut-website/src/main/app/voice-interview/interview-coverage.test.ts
index 84d329b5062..dc3846fefa4 100644
--- a/apps/petrinaut-website/src/main/app/voice-interview/interview-coverage.test.ts
+++ b/apps/petrinaut-website/src/main/app/voice-interview/interview-coverage.test.ts
@@ -1,6 +1,6 @@
 import { describe, expect, test } from "vitest";
 
-import { SWEEP_TOOL_NAME } from "@hashintel/brunch-agent-transport-aisdk/client-tools";
+import { SWEEP_TOOL_NAME } from "@hashintel/brunch-agent/client-tools";
 
 import { selectInterviewCoverage } from "./interview-coverage";
 
diff --git a/apps/petrinaut-website/src/main/app/voice-interview/interview-coverage.ts b/apps/petrinaut-website/src/main/app/voice-interview/interview-coverage.ts
index 5f1ef5b4164..c6e9f763bbc 100644
--- a/apps/petrinaut-website/src/main/app/voice-interview/interview-coverage.ts
+++ b/apps/petrinaut-website/src/main/app/voice-interview/interview-coverage.ts
@@ -1,4 +1,4 @@
-import { SWEEP_TOOL_NAME } from "@hashintel/brunch-agent-transport-aisdk/client-tools";
+import { SWEEP_TOOL_NAME } from "@hashintel/brunch-agent/client-tools";
 
 import { sweepOutputSchema } from "../brunch-sweep-output";
 
diff --git a/libs/@hashintel/brunch-agent/packages/core/src/client-tools.ts b/libs/@hashintel/brunch-agent/packages/core/src/client-tools.ts
index 3cea4ff89a6..b866300d288 100644
--- a/libs/@hashintel/brunch-agent/packages/core/src/client-tools.ts
+++ b/libs/@hashintel/brunch-agent/packages/core/src/client-tools.ts
@@ -2,5 +2,22 @@
  * Browser-safe source contracts for Brunch tools rendered by a host UI.
  */
 
-export { AskInput, AskSubmission } from "./ask-tool-contract";
-export { toolName, type ToolName } from "./naming";
+import * as v from "valibot";
+
+import { AskInput, AskSubmission } from "./ask-tool-contract";
+import { toolName } from "./naming";
+
+export { AskInput, AskSubmission, toolName };
+export type { ToolName } from "./naming";
+
+export const ASK_TOOL_NAME = toolName("ask");
+export const SWEEP_TOOL_NAME = toolName("sweep");
+
+export type BrunchAskInput = v.InferOutput<typeof AskInput>;
+export type BrunchAskOutput = v.InferOutput<typeof AskSubmission>;
+
+export const parseBrunchAskInput = (input: unknown): BrunchAskInput =>
+  v.parse(AskInput, input);
+
+export const parseBrunchAskOutput = (output: unknown): BrunchAskOutput =>
+  v.parse(AskSubmission, output);
diff --git a/libs/@hashintel/brunch-agent/packages/core/turbo.json b/libs/@hashintel/brunch-agent/packages/core/turbo.json
index d6f41dc7c53..5da6b59f7d6 100644
--- a/libs/@hashintel/brunch-agent/packages/core/turbo.json
+++ b/libs/@hashintel/brunch-agent/packages/core/turbo.json
@@ -14,6 +14,15 @@
     },
     "linear:graph": {
       "cache": false
+    },
+    "test:unit": {
+      "inputs": [
+        "$TURBO_DEFAULT$",
+        "$TURBO_ROOT$/apps/brunch-agent/**",
+        "$TURBO_ROOT$/libs/@hashintel/brunch-agent/**",
+        "!$TURBO_ROOT$/apps/brunch-agent/**/{.flue,.turbo,dist,node_modules}/**",
+        "!$TURBO_ROOT$/libs/@hashintel/brunch-agent/**/{.flue,.turbo,dist,node_modules}/**"
+      ]
     }
   }
 }
diff --git a/libs/@hashintel/brunch-agent/packages/transport-aisdk/.oxlintrc.json b/libs/@hashintel/brunch-agent/packages/transport-aisdk/.oxlintrc.json
index 8cf02a4f042..d7ed5324c29 100644
--- a/libs/@hashintel/brunch-agent/packages/transport-aisdk/.oxlintrc.json
+++ b/libs/@hashintel/brunch-agent/packages/transport-aisdk/.oxlintrc.json
@@ -22,6 +22,10 @@
           {
             "name": "@hashintel/petrinaut",
             "message": "Brunch libraries must not depend on Petrinaut implementations."
+          },
+          {
+            "name": "@hashintel/brunch-agent",
+            "message": "Brunch transports must remain independent of Brunch core."
           }
         ],
         "patterns": [
@@ -38,8 +42,8 @@
             "message": "Brunch transports must remain substrate-independent."
           },
           {
-            "group": ["@hashintel/brunch-agent-*"],
-            "message": "A transport may depend inward on the harness, not on Brunch extensions."
+            "group": ["@hashintel/brunch-agent/*", "@hashintel/brunch-agent-*"],
+            "message": "Brunch transports must remain independent of Brunch core and extensions."
           }
         ]
       }
diff --git a/libs/@hashintel/brunch-agent/packages/transport-aisdk/package.json b/libs/@hashintel/brunch-agent/packages/transport-aisdk/package.json
index 2d9591e4d43..9a58144ce85 100644
--- a/libs/@hashintel/brunch-agent/packages/transport-aisdk/package.json
+++ b/libs/@hashintel/brunch-agent/packages/transport-aisdk/package.json
@@ -10,10 +10,6 @@
       "types": "./src/index.ts",
       "import": "./dist/index.js"
     },
-    "./client-tools": {
-      "types": "./src/client-tools.ts",
-      "import": "./dist/client-tools.js"
-    },
     "./headers": {
       "types": "./src/headers.ts",
       "import": "./dist/headers.js"
@@ -27,7 +23,6 @@
     "test:unit": "vitest run"
   },
   "dependencies": {
-    "@hashintel/brunch-agent": "workspace:*",
     "ai": "6.0.182",
     "valibot": "1.4.2"
   },
diff --git a/libs/@hashintel/brunch-agent/packages/transport-aisdk/src/client-tools.ts b/libs/@hashintel/brunch-agent/packages/transport-aisdk/src/client-tools.ts
deleted file mode 100644
index a61e161d6dd..00000000000
--- a/libs/@hashintel/brunch-agent/packages/transport-aisdk/src/client-tools.ts
+++ /dev/null
@@ -1,23 +0,0 @@
-/**
- * Browser-safe wire contract for the Brunch tools a host UI executes.
- */
-
-import * as v from "valibot";
-
-import {
-  AskInput,
-  AskSubmission,
-  toolName,
-} from "@hashintel/brunch-agent/client-tools";
-
-export const ASK_TOOL_NAME = toolName("ask");
-export const SWEEP_TOOL_NAME = toolName("sweep");
-
-export type BrunchAskInput = v.InferOutput<typeof AskInput>;
-export type BrunchAskOutput = v.InferOutput<typeof AskSubmission>;
-
-export const parseBrunchAskInput = (input: unknown): BrunchAskInput =>
-  v.parse(AskInput, input);
-
-export const parseBrunchAskOutput = (output: unknown): BrunchAskOutput =>
-  v.parse(AskSubmission, output);
diff --git a/libs/@hashintel/brunch-agent/packages/transport-aisdk/vite.config.ts b/libs/@hashintel/brunch-agent/packages/transport-aisdk/vite.config.ts
index 369dc937a5d..a23d137f9ac 100644
--- a/libs/@hashintel/brunch-agent/packages/transport-aisdk/vite.config.ts
+++ b/libs/@hashintel/brunch-agent/packages/transport-aisdk/vite.config.ts
@@ -8,9 +8,6 @@ export default defineConfig({
   build: {
     lib: {
       entry: {
-        "client-tools": fileURLToPath(
-          new URL("src/client-tools.ts", import.meta.url),
-        ),
         headers: fileURLToPath(new URL("src/headers.ts", import.meta.url)),
         index: fileURLToPath(new URL("src/index.ts", import.meta.url)),
       },
@@ -18,7 +15,7 @@ export default defineConfig({
       formats: ["es"],
     },
     rolldownOptions: {
-      external: [/^@hashintel\/brunch-agent(?:\/.*)?$/u, "ai", "valibot"],
+      external: ["ai", "valibot"],
     },
     sourcemap: true,
   },
diff --git a/yarn.config.cjs b/yarn.config.cjs
index 4270b58385e..79fd15816d2 100644
--- a/yarn.config.cjs
+++ b/yarn.config.cjs
@@ -40,6 +40,10 @@ const ignoredWorkspaces = [];
 
 const allowedGitDependencies = [];
 
+const brunchAgentCore = "@hashintel/brunch-agent";
+const brunchAgentTransportPrefix = `${brunchAgentCore}-transport-`;
+const brunchSubstrateScopes = ["@earendil-works/", "@flue/"];
+
 /**
  * Lifecycle scripts which Yarn runs as part of `yarn install`.
  */
@@ -319,6 +323,30 @@ function enforceNoInstallScripts({ Yarn }) {
   }
 }
 
+/**
+ * Keeps transport packages independent of Brunch mechanism and substrates.
+ *
+ * @param {Context} context - The Yarn constraint context.
+ */
+function enforceBrunchTransportBoundary({ Yarn }) {
+  for (const dependency of Yarn.dependencies()) {
+    if (
+      !dependency.workspace.ident.startsWith(brunchAgentTransportPrefix) ||
+      (dependency.ident !== brunchAgentCore &&
+        !dependency.ident.startsWith(`${brunchAgentCore}-`) &&
+        !brunchSubstrateScopes.some((scope) =>
+          dependency.ident.startsWith(scope),
+        ))
+    ) {
+      continue;
+    }
+
+    dependency.error(
+      `${dependency.workspace.ident} is a transport and cannot depend on ${dependency.ident}`,
+    );
+  }
+}
+
 module.exports = defineConfig({
   async constraints(context) {
     enforceConsistentDependenciesAcrossTheProject(context);
@@ -326,5 +354,6 @@ module.exports = defineConfig({
     enforceProtocols(context);
     enforceDevDependenciesAreProperlyDeclared(context);
     enforceNoInstallScripts(context);
+    enforceBrunchTransportBoundary(context);
   },
 });
diff --git a/yarn.lock b/yarn.lock
index 91401d202c6..6af226a8342 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -919,6 +919,7 @@ __metadata:
   dependencies:
     "@ai-sdk/openai": "npm:3.0.63"
     "@fast-check/vitest": "npm:0.4.1"
+    "@hashintel/brunch-agent": "workspace:*"
     "@hashintel/brunch-agent-transport-aisdk": "workspace:*"
     "@hashintel/ds-components": "workspace:*"
     "@hashintel/ds-helpers": "workspace:*"
@@ -7437,7 +7438,6 @@ __metadata:
   version: 0.0.0-use.local
   resolution: "@hashintel/brunch-agent-transport-aisdk@workspace:libs/@hashintel/brunch-agent/packages/transport-aisdk"
   dependencies:
-    "@hashintel/brunch-agent": "workspace:*"
     "@types/node": "npm:22.18.13"
     "@typescript/native-preview": "npm:7.0.0-dev.20260511.1"
     ai: "npm:6.0.182"