diff --git a/BACKLOG.md b/BACKLOG.md
index 9d210e28..e9043132 100644
--- a/BACKLOG.md
+++ b/BACKLOG.md
@@ -107,7 +107,8 @@ CC-001/CC-002 were consumed by PR #24 fix bundle inline, with no standalone entr
 | CC-568 | 🟢 someday | `/mem-distill` Case→Strategy 機械式提升：對 `episodes.jsonl` 既有結構化欄位做 count/cluster 門檻判定，取代逐次主觀「感覺像 pattern」的判斷；依賴 [[CC-567]] 的 outcome 證據決定是否值得做（2026-08-25 memory 架構設計討論） | memory/DX | 2026-08-25 | — | P2 | retrieval |
 | CC-569 | 🟢 someday | `pmctl task` / `context pack` 擴充 working-memory 敘事欄位（`selected_memories`／`rejected_paths`／`blockers`／`next_action`）：延伸既有 schema，不新建第二個「現在在幹嘛」真相來源；依賴 [[CC-567]] 證明有價值後再排（2026-08-25 memory 架構設計討論） | memory/DX | 2026-08-25 | — | P2 | design |
 | CC-570 | 🟢 someday | Fact/Case/Strategy `memory_function`／`memory_subtype` metadata 分類法：先蒐集 [[CC-567]] 的 applied/outcome 證據，再決定值不值得建分類機制——不憑直覺先建立稅務式標籤（2026-08-25 memory 架構設計討論；外部文章優先序建議相反，本 repo 刻意反過來） | memory/DX | 2026-08-25 | — | P3 | retrieval |
-| CC-571 | 🔵 active | `_ctx_fts_rebuild`／`_ctx_index_file` 共用的 sqlite atomic-script 缺口：DROP+CREATE+INSERT 未加 `-bail`（實測 sqlite3 CLI 預設不會在錯誤時中止，單靠 BEGIN/COMMIT 不足）、呼叫端不檢查回傳值、`_ctx_index_file` 還有第三個獨立 bug（`rm -f` 蓋掉 sqlite3 真實 exit code）；`/simplify` altitude review 抓到手足函式同缺陷，範圍已擴大涵蓋兩者（[[CC-548]] spike 的 Open risks 側面發現，非本票 tokenizer 範圍） | memory/ops | 2026-08-26 | — | P2 | hygiene |
+| CC-571 | ✅ done | `_ctx_fts_rebuild`／`_ctx_index_file` 共用的 sqlite atomic-script 缺口：DROP+CREATE+INSERT 未加 `-bail`（實測 sqlite3 CLI 預設不會在錯誤時中止，單靠 BEGIN/COMMIT 不足）、呼叫端不檢查回傳值、`_ctx_index_file` 還有第三個獨立 bug（`rm -f` 蓋掉 sqlite3 真實 exit code）；`/simplify` altitude review 抓到手足函式同缺陷，範圍已擴大涵蓋兩者（[[CC-548]] spike 的 Open risks 側面發現，非本票 tokenizer 範圍） | memory/ops | 2026-08-26 | pr:#539 | P2 | hygiene |
+| CC-572 | ✅ done | pr-gate synthesis retry（sequential／parallel 兩條路徑）留下已存在但 0 bytes 的 `$OUTPUT_FILE`，executor 的 patch 工具仍可能選擇 Update File 而非 Add File 語意，對空內容找不到 context line 而崩潰（`apply_patch verification failed`）；CC-571 gate saga 連續四輪協定失敗實測發現（2026-08-26） | gate/ops | 2026-08-26 | pr:#541 | P2 | hygiene |
 
 ---
 
@@ -3335,7 +3336,7 @@ machinery，是憑一篇文章的直覺蓋機制，屬於本 repo 已經吃過
 
 ---
 
-## CC-571 — sqlite atomic-script 缺口：`_ctx_fts_rebuild`／`_ctx_index_file` 🔵 active
+## CC-571 — sqlite atomic-script 缺口：`_ctx_fts_rebuild`／`_ctx_index_file`
 
 **Problem**: `runtime/lib/pmctl-context.sh` 的 `_ctx_fts_rebuild()` 對
 `content_fts` 做 `DROP TABLE` → `CREATE VIRTUAL TABLE` → 兩個 `INSERT ... SELECT`，
@@ -3393,4 +3394,57 @@ best-effort 加速層，宣稱「re-indexed」等於說謊）。新增對應 reg
 `runtime/lib/memory.sh` 的 `memory_usage_commit`（既有的 `-bail` atomic-script
 先例，本票的 helper 命名與理由都直接引用它，而非各自重新推導）。
 
+**Update 2026-08-26（done，pr:#539）**：pr-gate 5 輪後 GO（critic／qa-tester／
+architecture-reviewer／security-reviewer 全數 approve）。前兩輪是真實發現並已修正：
+round 1 critic-F001——stderr 有印降級訊息，但 stdout 的成功摘要行本身仍是無條件
+「N indexed, M skipped」，對只看 stdout／exit code 的呼叫端是矛盾摘要，改成把降級
+狀態直接併入 stdout 摘要行本身；round 2 critic-F001——首次建置索引失敗時（rebuild
+前 `content_fts` 根本不存在），訊息卻說「現有索引維持」，改為依 rebuild 前是否已有
+`content_fts` 分支措辭。中間另有 3 輪是 gate 執行環境本身的 synthesis 協定不穩定
+（`apply_patch` 在同一份 result 檔案上多次操作互相衝突、`findings_union`/
+`disagreement` 結構不一致），與程式碼無關，重跑收斂。`tests/bin/run-all-tests.sh`
+104 passed 0 failed。狀態旗標本次於 main 更新後立即補記——同一 session 已因此類
+漏更新撞過三次（CC-567／CC-533／CC-015），這次差點又漏，補上教訓：**合併前**就該
+在 PR 裡帶上狀態翻轉，合併後才想起來永遠比合併前想起來更容易忘記。
+
+---
+
+## CC-572 — pr-gate synthesis 重試留下空但存在的 result 檔案，patch 工具語意混淆
+
+**Problem**: CC-571 的 pr-gate saga 連續遇到 4 輪協定失敗，其中兩類錯誤反覆出現：
+`apply_patch verification failed: invalid patch: multiple operations target <file>`
+與 `Failed to find expected lines in <file>: ...`。追查後發現：sequential 模式的
+synthesis 重試（`runtime/bin/pr-gate.sh` 約 line 2748）在重試前用 `: > "$OUTPUT_FILE"`
+把結果檔案**清空但保留路徑存在**；parallel 模式的 synthesis 重試（約 line 3600 附近的
+迴圈）則完全沒有清空或移除，重試時 `$OUTPUT_FILE` 仍是第一次嘗試的完整內容。兩者都
+讓 executor 的 patch 工具面對一個「路徑存在」的檔案，可能因此選擇 `Update File`
+（需要定位既有內容做編輯）而非 `Add File`（單純新建）語意——對 0 bytes 或即將整份
+重寫的檔案，`Update File` 語意本質上找不到可定位的 context line，因而崩潰。
+
+**Why**: reviewer-protocol 的重試路徑（同檔案內，寫到全新的
+`reviewer-<name>-<ts>-retry1.md` 路徑）從未出現過這個問題——因為那個路徑保證是全新
+的，patch 工具沒有選錯語意的空間。Synthesis 的兩條重試路徑都固定用同一個
+`$OUTPUT_FILE`（這個路徑本身是使用者看得到的 canonical gate 結果路徑，不能像
+reviewer 重試一樣改路徑），只能改成每次重試前把該路徑**整個移除**（而非清空），
+逼 patch 工具只能選擇 `Add File`。
+
+**Requirement**:
+1. 兩條 synthesis 重試路徑（sequential／parallel）在重新 dispatch 前，都必須讓
+   `$OUTPUT_FILE` 這個路徑真正不存在（而非僅清空內容），逼 patch 工具走
+   `Add File` 而非 `Update File`。
+2. Regression fixtures 驗證重試發生時 `$OUTPUT_FILE` 在第二次 dispatch **開始前**
+   確實不存在，且既有 synthesis-protocol 測試全數維持綠燈。
+
+**Non-goals**: 不改變 synthesis 重試次數（維持 1 次，不重新開放 CC-544 已被否決的
+「重試把失敗變成通過」爭議——本票的重試機制本來就誠實回報協定失敗，不受影響）；
+不修改 reviewer-protocol 既有的重試機制（已經是正確模式，不需要改）；不嘗試修正
+codex 自己的 apply_patch 工具實作（不在本 repo 控制範圍）。
+
+**Cross-link**: [[CC-571]]（gate saga 實測發現本問題的來源）。
+
+**Update 2026-08-26（done，pr:#541）**：兩條路徑都已修好，新增迴歸測試直接斷言
+重試發生時該路徑真的不存在（而非僅清空）。pr-gate 首輪 GO（未在該次 gate run
+自身觸發 synthesis retry，修復是靠直接比對過往失敗 log 的根因＋白箱迴歸測試
+驗證，非現場實戰）。`tests/bin/run-all-tests.sh` 104 passed 0 failed。
+
 ---
diff --git a/runtime/bin/pr-gate.sh b/runtime/bin/pr-gate.sh
index e383de7b..f06d47a4 100755
--- a/runtime/bin/pr-gate.sh
+++ b/runtime/bin/pr-gate.sh
@@ -804,6 +804,18 @@ gate_dispatch_command() {
   fi
 }
 
+# Removing the path (not truncating it) matters -- observed in production,
+# an executor's patch tool can choose an "Update File" operation (which
+# locates existing content to edit) against a path that still EXISTS on
+# disk, even truncated to 0 bytes -- and that operation then fails
+# ("Failed to find expected lines", "invalid patch: multiple operations
+# target <file>") because there is no content to locate. Only removing the
+# path forces an unambiguous "Add File", matching the reviewer-retry path's
+# already-reliable brand-new-filename behavior.
+gate_clear_retry_target() {
+  rm -f "$1"
+}
+
 # Every supported executor now dispatches an INDEPENDENT subprocess (codex `codex
 # exec`, claude headless `claude --print`) and writes the result in-process, which
 # the gate then integrity-checks. This flag is the seam where a future
@@ -2742,10 +2754,11 @@ BRIEF_EOF
   for _seq_attempt in 1 2; do
   if [[ "$_seq_attempt" -eq 2 ]]; then
     # The brief has the executor CREATE the file on the first reviewer and
-    # APPEND for the rest, so a retry must start from an empty document:
+    # APPEND for the rest, so a retry must start from a clean slate:
     # appending to a rejected, half-ordered one compounds the defect the
-    # retry exists to fix.
-    : > "$OUTPUT_FILE"
+    # retry exists to fix. See gate_clear_retry_target for why this removes
+    # the path rather than truncating it.
+    gate_clear_retry_target "$OUTPUT_FILE"
     # Same trust boundary as the parallel retry: the reason quotes ids read
     # from the rejected artifact, so flatten newlines and bound the length
     # before it becomes a YAML block scalar in a privileged brief.
@@ -2753,7 +2766,7 @@ BRIEF_EOF
     _seq_reason_line="${_seq_reason_line//$'\r'/ }"
     [[ "${#_seq_reason_line}" -le 800 ]] \
       || _seq_reason_line="${_seq_reason_line:0:800}~"
-    printf '\ncorrection_retry: |\n  The first attempt was REJECTED for exactly this reason:\n\n    %s\n\n  %s has been emptied. Rebuild it completely, in the required section\n  order, from the same reviewer evidence -- fix that specific defect and do\n  not change any other section to compensate.\n' \
+    printf '\ncorrection_retry: |\n  The first attempt was REJECTED for exactly this reason:\n\n    %s\n\n  %s has been removed. Rebuild it completely from scratch, in the\n  required section order, from the same reviewer evidence -- fix that\n  specific defect and do not change any other section to compensate.\n' \
       "$_seq_reason_line" "$OUTPUT_FILE" >> "$BRIEF_FILE"
     say '  [sequential] retrying once after %s.\n' "$_seq_reason"
   fi
@@ -3619,6 +3632,15 @@ SBRIEF_P2
         || _synthesis_reason_line="${_synthesis_reason_line:0:800}~"
       printf '\ncorrection_retry: |\n  The first synthesis attempt was REJECTED for exactly this reason:\n\n    %s\n\n  Fix that specific defect. Copied coverage/inventory/test-gap fields are\n  restored by the shell from the embedded reviewer_result_v1 documents; do not\n  retype them. Rebuild grouping, disagreement, confirmation, and seed fields\n  from those same documents -- do not change any other section to compensate.\n' \
         "$_synthesis_reason_line" >> "$SYNTHESIS_BRIEF"
+      # Unlike the reviewer-protocol retry above (which writes to a
+      # brand-new path, e.g. reviewer-<name>-<ts>-retry1.md), the synthesis
+      # retry re-dispatches to the SAME fixed $OUTPUT_FILE path. See
+      # gate_clear_retry_target for why this removes the path rather than
+      # leaving attempt 1's content in place. The brief already
+      # tells the model to rebuild every field fresh from the embedded
+      # reviewer context, so nothing here depends on attempt 1's on-disk
+      # content surviving into attempt 2.
+      gate_clear_retry_target "$OUTPUT_FILE"
     fi
     say '  [synthesis attempt %d] running PM consolidation...\n' "$_synthesis_attempt"
     SYNTHESIS_DISPATCH_CMD="$(gate_dispatch_command "$EXECUTOR" "$SYNTHESIS_BRIEF" "$WORK_DIR" "$DISPATCH_MODEL" "$DISPATCH_SANDBOX" "$DISPATCH_APPROVAL" "$TIMEOUT" "$DISPATCH_ISOLATION" "$DISPATCH_EFFORT")" || exit 2
diff --git a/tests/shell/test-pr-gate.sh b/tests/shell/test-pr-gate.sh
index 5096e7ef..920989cc 100755
--- a/tests/shell/test-pr-gate.sh
+++ b/tests/shell/test-pr-gate.sh
@@ -120,6 +120,27 @@ done
 reviewer_name="$(awk '$1 == "Reviewer:" { print $2; exit }' "$brief_file")"
 : "${reviewer_name:=stub-reviewer}"
 
+# Record whether the synthesis/sequential result path exists on disk at the
+# very start of THIS dispatch (before this stub or anything else in this
+# invocation touches it) -- the property a synthesis retry must uphold is
+# that the path is gone (not just empty) before the retry's own write
+# begins. Must run before any other block below that might create the file.
+if [[ -n "${CODEX_GATE_CAPTURE_OUTPUT_EXISTS_DIR:-}" ]] \
+    && { [[ "$brief_file" == *-synthesis.md ]] || grep -q '^goal: Sequential ' "$brief_file"; }; then
+  _output_exists_path=$(grep -o '\- new:.*' "$brief_file" | head -1 | awk '{print $NF}')
+  mkdir -p "$CODEX_GATE_CAPTURE_OUTPUT_EXISTS_DIR"
+  # Each gate run's synthesis dispatches at most twice (initial + one
+  # retry), so a fixed first/second pair of files is simpler than a
+  # counted/globbed sequence for a caller that only ever expects two checks.
+  _output_exists_state="exists"
+  [[ -n "$_output_exists_path" && -e "$_output_exists_path" ]] || _output_exists_state="absent"
+  if [[ ! -e "$CODEX_GATE_CAPTURE_OUTPUT_EXISTS_DIR/first" ]]; then
+    printf '%s\n' "$_output_exists_state" > "$CODEX_GATE_CAPTURE_OUTPUT_EXISTS_DIR/first"
+  else
+    printf '%s\n' "$_output_exists_state" > "$CODEX_GATE_CAPTURE_OUTPUT_EXISTS_DIR/second"
+  fi
+fi
+
 # CC-541: capture whatever QA_RULES_DIR value (if any) this dispatch inherited,
 # so tests can assert pr-gate.sh's host-side resolution reached the reviewer
 # subprocess env without needing a real codex model to interpret it.
@@ -11887,6 +11908,65 @@ test_parallel_synthesis_retry_brief_bounds_long_reason() {
   pass "$name"
 }
 
+# Behavior: a synthesis retry (either mode) must remove $OUTPUT_FILE before
+# re-dispatching, not just leave the first attempt's content sitting on
+# disk. Observed in production: an executor's patch tool can choose an
+# "Update File" operation against a path that still exists (even truncated
+# to empty), and that operation then fails outright because there is no
+# matching content to locate -- a hard tool failure unrelated to the
+# actual synthesis content. Only full removal forces an unambiguous
+# "Add File" the same way a brand-new path would.
+# Steps: force a first-attempt synthesis failure (existing malformed-seed
+# mutation); the capture hook in the stub records, at the very start of
+# EACH synthesis dispatch (before the stub or anything else writes to the
+# path), whether $OUTPUT_FILE existed at that instant. Assert the first
+# check says "exists" (the reviewer-append step already wrote content before
+# synthesis attempt 1 runs) and the second (retry) check says "absent".
+# Shared by both modes because the property under test -- and the fixture
+# setup to exercise it -- is identical; only --mode differs. Sequential and
+# parallel dispatch through separately-authored retry loops in
+# runtime/bin/pr-gate.sh (the sequential one used to truncate the file
+# rather than remove it), so both are exercised as their own named result.
+_test_synthesis_retry_removes_output_file_before_redispatch() {
+  local mode="$1" test_prefix="$2"
+  local name="${test_prefix}/retry-removes-output-file-before-redispatch"
+  should_run "$name" || return 0
+  local dir="$TMP_ROOT/$name" home="$TMP_ROOT/$name/home"
+  local repo="$TMP_ROOT/$name/repo" runner="$TMP_ROOT/$name/runner"
+  local out="$TMP_ROOT/$name/out" err="$TMP_ROOT/$name/err" code=0
+  local checks="$TMP_ROOT/$name/checks"
+  mkdir -p "$dir" "$checks"
+  create_runner "$runner"
+  create_agents "$home" critic qa-tester
+  create_repo "$repo" docs
+  set +e
+  CODEX_GATE_STUB_SYNTHESIS_PROTOCOL_MUTATION=malformed-seed \
+    CODEX_GATE_STUB_SYNTHESIS_PROTOCOL_MUTATION_ONLY_FIRST=1 \
+    CODEX_GATE_CAPTURE_OUTPUT_EXISTS_DIR="$checks" \
+    run_gate "$home" "$runner" "$repo" "$out" "$err" \
+      --base main --reviewers critic,qa-tester --mode "$mode"
+  code=$?
+  set -e
+  [[ "$code" -eq 0 ]] || { fail "$name" "did not recover: code=$code $(tail -n 5 "$err" 2>/dev/null)"; return; }
+  [[ -f "$checks/second" ]] || {
+    fail "$name" "second dispatch's existence check was not captured: $(find "$checks" -maxdepth 1 -printf '%P ' 2>/dev/null)"
+    return
+  }
+  assert_file_contains "$name" "$checks/first" "exists" || return
+  assert_file_contains "$name" "$checks/second" "absent" || return
+  pass "$name"
+}
+
+# Behavior: parallel-mode wrapper for the shared check above.
+test_parallel_synthesis_retry_removes_output_file_before_redispatch() {
+  _test_synthesis_retry_removes_output_file_before_redispatch parallel synthesis-protocol
+}
+
+# Behavior: sequential-mode wrapper for the shared check above.
+test_sequential_synthesis_retry_removes_output_file_before_redispatch() {
+  _test_synthesis_retry_removes_output_file_before_redispatch sequential sequential-protocol
+}
+
 # Behavior: a stale subject binding is NOT retried in sequential mode.
 # Steps: bind the synthesis to a different scope digest, then assert the gate
 # refuses the retry and says so.
@@ -12985,6 +13065,8 @@ run_test test_synthesis_protocol_diagnostics_name_the_defect
 run_test test_synthesis_protocol_diagnostics_neutralize_injected_ids
 run_test test_parallel_synthesis_retry_brief_carries_reason
 run_test test_parallel_synthesis_retry_brief_bounds_long_reason
+run_test test_parallel_synthesis_retry_removes_output_file_before_redispatch
+run_test test_sequential_synthesis_retry_removes_output_file_before_redispatch
 run_test test_sequential_protocol_recovers_on_retry
 run_test test_sequential_protocol_refuses_stale_subject_retry
 run_test test_sequential_retry_brief_bounds_long_reason