diff --git a/src/resources/extensions/gsd/auto-post-unit.ts b/src/resources/extensions/gsd/auto-post-unit.ts
index b0bd77dd2..dc710830f 100644
--- a/src/resources/extensions/gsd/auto-post-unit.ts
+++ b/src/resources/extensions/gsd/auto-post-unit.ts
@@ -25,6 +25,7 @@ import {
   buildTaskFileName,
 } from "./paths.js";
 import { invalidateAllCaches } from "./cache.js";
+import { rebuildState } from "./doctor.js";
 import { parseUnitId } from "./unit-id.js";
 import { closeoutUnit, type CloseoutOptions } from "./auto-unit-closeout.js";
 import {
@@ -367,6 +368,12 @@ export async function postUnitPreVerification(pctx: PostUnitContext, opts?: PreV
       }
     });
 
+    // Keep the on-disk STATE.md aligned with the live derived state after
+    // ordinary unit completion, before any worktree state is synced back.
+    await runSafely("postUnit", "state-rebuild", async () => {
+      await rebuildState(s.basePath);
+    });
+
     // Sync worktree state back to project root (skipped for lightweight sidecars)
     if (!opts?.skipWorktreeSync && s.originalBasePath && s.originalBasePath !== s.basePath) {
       await runSafely("postUnit", "worktree-sync", () => {
diff --git a/src/resources/extensions/gsd/tests/post-unit-state-rebuild.test.ts b/src/resources/extensions/gsd/tests/post-unit-state-rebuild.test.ts
new file mode 100644
index 000000000..43e73388d
--- /dev/null
+++ b/src/resources/extensions/gsd/tests/post-unit-state-rebuild.test.ts
@@ -0,0 +1,34 @@
+/**
+ * Regression test for #3869: normal post-unit flow should rebuild STATE.md
+ * before syncing worktree state back to the project root.
+ */
+
+import test from "node:test";
+import assert from "node:assert/strict";
+import { readFileSync } from "node:fs";
+import { join } from "node:path";
+
+const source = readFileSync(join(import.meta.dirname, "..", "auto-post-unit.ts"), "utf-8");
+
+test("auto-post-unit imports rebuildState", () => {
+  assert.ok(
+    source.includes('import { rebuildState } from "./doctor.js";'),
+    "auto-post-unit.ts should import rebuildState from doctor.ts",
+  );
+});
+
+test("postUnitPreVerification rebuilds STATE.md before worktree sync", () => {
+  const fnStart = source.indexOf("export async function postUnitPreVerification");
+  assert.ok(fnStart > 0, "postUnitPreVerification should exist");
+
+  const section = source.slice(fnStart, fnStart + 8000);
+  const rebuildIdx = section.indexOf('await runSafely("postUnit", "state-rebuild"');
+  const syncIdx = section.indexOf('await runSafely("postUnit", "worktree-sync"');
+
+  assert.ok(rebuildIdx > 0, "postUnitPreVerification should rebuild STATE.md after unit completion");
+  assert.ok(syncIdx > 0, "postUnitPreVerification should sync worktree state back to the project root");
+  assert.ok(
+    rebuildIdx < syncIdx,
+    "STATE.md rebuild should happen before worktree sync so synced state is fresh",
+  );
+});