diff --git a/src/resources/extensions/gsd/auto-prompts.ts b/src/resources/extensions/gsd/auto-prompts.ts
index 6f1b376c4..8501475c1 100644
--- a/src/resources/extensions/gsd/auto-prompts.ts
+++ b/src/resources/extensions/gsd/auto-prompts.ts
@@ -469,6 +469,17 @@ export async function checkNeedsReassessment(
 
   if (hasAssessment) return null;
 
+  // Fallback: check the expected path directly via existsSync.
+  // resolveSliceFile relies on directory listing (readdirSync) which may not
+  // reflect a freshly written file in git worktree directories on some
+  // filesystems (observed on macOS APFS). A direct existsSync on the
+  // constructed path bypasses directory listing entirely. (#1112)
+  const sliceDir = resolveSlicePath(base, mid, lastCompleted.id);
+  if (sliceDir) {
+    const directPath = join(sliceDir, `${lastCompleted.id}-ASSESSMENT.md`);
+    if (existsSync(directPath)) return null;
+  }
+
   // Also need a summary to reassess against
   const summaryFile = resolveSliceFile(base, mid, lastCompleted.id, "SUMMARY");
   const hasSummary = !!(summaryFile && await loadFile(summaryFile));
diff --git a/src/resources/extensions/gsd/tests/reassess-detection.test.ts b/src/resources/extensions/gsd/tests/reassess-detection.test.ts
new file mode 100644
index 000000000..aef393b06
--- /dev/null
+++ b/src/resources/extensions/gsd/tests/reassess-detection.test.ts
@@ -0,0 +1,154 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import { mkdirSync, writeFileSync, rmSync } from "node:fs";
+import { join } from "node:path";
+import { tmpdir } from "node:os";
+import { randomUUID } from "node:crypto";
+
+import { checkNeedsReassessment } from "../auto-prompts.ts";
+import { invalidateAllCaches } from "../cache.ts";
+import type { GSDState } from "../types.ts";
+
+function makeTmpBase(): string {
+  const base = join(tmpdir(), `gsd-test-reassess-${randomUUID()}`);
+  mkdirSync(join(base, ".gsd", "milestones", "M001", "slices", "S01", "tasks"), { recursive: true });
+  mkdirSync(join(base, ".gsd", "milestones", "M001", "slices", "S02", "tasks"), { recursive: true });
+  return base;
+}
+
+function cleanup(base: string): void {
+  try { rmSync(base, { recursive: true, force: true }); } catch { /* */ }
+}
+
+function writeRoadmap(base: string, content: string): void {
+  writeFileSync(join(base, ".gsd", "milestones", "M001", "M001-ROADMAP.md"), content);
+}
+
+function writeSummary(base: string, sid: string): void {
+  writeFileSync(
+    join(base, ".gsd", "milestones", "M001", "slices", sid, `${sid}-SUMMARY.md`),
+    `---\nid: ${sid}\n---\n# ${sid} Summary\nDone.`,
+  );
+}
+
+function writeAssessment(base: string, sid: string): void {
+  writeFileSync(
+    join(base, ".gsd", "milestones", "M001", "slices", sid, `${sid}-ASSESSMENT.md`),
+    `# ${sid} Assessment\nNo changes needed.`,
+  );
+}
+
+const ROADMAP_S01_DONE_S02_TODO = `# M001 Roadmap
+## Slices
+- [x] **S01: First** \`risk:high\` \`depends:[]\`
+- [ ] **S02: Second** \`risk:medium\` \`depends:[S01]\`
+`;
+
+const dummyState: GSDState = {
+  phase: "executing",
+  activeMilestone: { id: "M001", title: "Test" },
+  activeSlice: { id: "S02", title: "Second" },
+  activeTask: null,
+  recentDecisions: [],
+  blockers: [],
+  nextAction: "",
+  registry: [{ id: "M001", title: "Test", status: "active" }],
+};
+
+// ─── checkNeedsReassessment: returns null when assessment exists ─────────
+
+test("checkNeedsReassessment returns null when assessment file exists", async () => {
+  const base = makeTmpBase();
+  try {
+    invalidateAllCaches();
+    writeRoadmap(base, ROADMAP_S01_DONE_S02_TODO);
+    writeSummary(base, "S01");
+    writeAssessment(base, "S01");
+
+    const result = await checkNeedsReassessment(base, "M001", dummyState);
+    assert.strictEqual(result, null, "should return null when assessment exists");
+  } finally {
+    cleanup(base);
+  }
+});
+
+// ─── checkNeedsReassessment: returns sliceId when assessment missing ─────
+
+test("checkNeedsReassessment returns sliceId when assessment is missing", async () => {
+  const base = makeTmpBase();
+  try {
+    invalidateAllCaches();
+    writeRoadmap(base, ROADMAP_S01_DONE_S02_TODO);
+    writeSummary(base, "S01");
+    // No assessment written
+
+    const result = await checkNeedsReassessment(base, "M001", dummyState);
+    assert.deepStrictEqual(result, { sliceId: "S01" });
+  } finally {
+    cleanup(base);
+  }
+});
+
+// ─── checkNeedsReassessment: returns null when no summary exists ─────────
+
+test("checkNeedsReassessment returns null when summary is missing", async () => {
+  const base = makeTmpBase();
+  try {
+    invalidateAllCaches();
+    writeRoadmap(base, ROADMAP_S01_DONE_S02_TODO);
+    // No summary, no assessment
+
+    const result = await checkNeedsReassessment(base, "M001", dummyState);
+    assert.strictEqual(result, null, "should return null — can't reassess without summary");
+  } finally {
+    cleanup(base);
+  }
+});
+
+// ─── checkNeedsReassessment: detects assessment written after cache ──────
+// This is the core regression test for #1112: the assessment file is written
+// to disk AFTER the path cache was populated (simulating the worktree race
+// condition where readdirSync doesn't see a freshly written file).
+
+test("checkNeedsReassessment detects assessment written after initial cache population", async () => {
+  const base = makeTmpBase();
+  try {
+    writeRoadmap(base, ROADMAP_S01_DONE_S02_TODO);
+    writeSummary(base, "S01");
+
+    // First call: no assessment exists — populates internal caches
+    invalidateAllCaches();
+    const before = await checkNeedsReassessment(base, "M001", dummyState);
+    assert.deepStrictEqual(before, { sliceId: "S01" }, "should need reassessment initially");
+
+    // Now write the assessment WITHOUT clearing caches.
+    // This simulates the race condition: the agent wrote the file, but the
+    // directory listing cache still has the old state.
+    writeAssessment(base, "S01");
+
+    // Second call: the file exists on disk but caches may be stale.
+    // With the fix (#1112), the existsSync fallback should detect it.
+    invalidateAllCaches();
+    const after = await checkNeedsReassessment(base, "M001", dummyState);
+    assert.strictEqual(after, null, "should return null — assessment exists on disk (fallback check)");
+  } finally {
+    cleanup(base);
+  }
+});
+
+// ─── checkNeedsReassessment: returns null when all slices done ───────────
+
+test("checkNeedsReassessment returns null when all slices are complete", async () => {
+  const base = makeTmpBase();
+  try {
+    invalidateAllCaches();
+    const allDone = `# M001 Roadmap\n## Slices\n- [x] **S01: First** \`risk:high\` \`depends:[]\`\n- [x] **S02: Second** \`risk:medium\` \`depends:[S01]\`\n`;
+    writeRoadmap(base, allDone);
+    writeSummary(base, "S02");
+
+    const result = await checkNeedsReassessment(base, "M001", dummyState);
+    assert.strictEqual(result, null, "should return null — all slices done, no point reassessing");
+  } finally {
+    cleanup(base);
+  }
+});