diff --git a/.github/scripts/qwen-triage-workflow.test.mjs b/.github/scripts/qwen-triage-workflow.test.mjs
index f21b2c562b..22cb58192d 100644
--- a/.github/scripts/qwen-triage-workflow.test.mjs
+++ b/.github/scripts/qwen-triage-workflow.test.mjs
@@ -1014,9 +1014,14 @@ describe('qwen-triage: flakiness gate (#9125)', () => {
     // executes, so it is a changed test file exactly like M.
     assert.match(
       recordStep.run,
-      /^\s*git -c core\.quotePath=false diff -z --name-only --diff-filter=ACMRT 'HEAD\^1' HEAD \\\n\s*> "\$GATE_HOME\/files-all"$/m,
+      /^\s*git -c core\.quotePath=false diff -z --name-only --diff-filter=ACMRT "\$BASE_OID" HEAD \\\n\s*> "\$GATE_HOME\/files-all"$/m,
       'the NUL diff must flow straight into its file — $( ) strips NUL bytes, a pipeline swallows the exit status',
     );
+    assert.match(
+      recordStep.run,
+      /^\s*BASE_OID="\$\(cat "\$\{RUNNER_TEMP:\?\}\/verify-base-oid"\)"$/m,
+      'the record step must diff against the base OID captured while .git was root-owned, not re-resolve HEAD^1',
+    );
     assert.ok(
       recordStep.run.includes(
         "grep -zE '\\.(test|spec)\\.(ts|tsx|js|jsx|mjs|cjs|mts|cts)$'",
diff --git a/.github/workflows/qwen-triage.yml b/.github/workflows/qwen-triage.yml
index 1236cfbda8..0e9f9493f5 100644
--- a/.github/workflows/qwen-triage.yml
+++ b/.github/workflows/qwen-triage.yml
@@ -2975,7 +2975,20 @@ jobs:
           # T (typechange) included: a symlink->regular flip changes what
           # the runner executes, so it is a changed test file exactly
           # like M — excluding it silently drops the file from the gate.
-          git -c core.quotePath=false diff -z --name-only --diff-filter=ACMRT 'HEAD^1' HEAD \
+          # Diff against the base OID the "Pin agent inputs" step recorded
+          # while .git was still root-owned, never `HEAD^1` again: this
+          # step runs in the env -i scrubbed child, and resolving the `^1`
+          # parent there intermittently fails with "Could not access
+          # 'HEAD^1'" on the persistent pool — the shallow merge-ref object
+          # store is left in a state prior --depth=2 fetches made
+          # unreadable. The OID is content-addressed and needs no parent
+          # walk, so the diff works from the already-captured value.
+          BASE_OID="$(cat "${RUNNER_TEMP:?}/verify-base-oid")"
+          case "$BASE_OID" in
+            [0-9a-f][0-9a-f][0-9a-f][0-9a-f][0-9a-f][0-9a-f][0-9a-f][0-9a-f]*) ;;
+            *) echo "::error::No trusted base OID recorded; refusing to record the flakiness-gate file list."; exit 1 ;;
+          esac
+          git -c core.quotePath=false diff -z --name-only --diff-filter=ACMRT "$BASE_OID" HEAD \
             > "$GATE_HOME/files-all"
           # .mts/.cts included: vitest's default include set collects them.
           # Only a no-match (status 1) may yield an empty list: a grep