refactor(skills): simplify checkpoint locking

skills/develop/develop-workflow/references/evidence-and-recovery.md

@@ -13,7 +13,7 @@ node skills/develop/develop-workflow/scripts/checkpoint-record.mjs \
   <record.md> --input <candidate.md> --expected-sha256 <current-digest>
 ```
 
-Omit `--expected-sha256` only for first creation; require an absent target. Commit the initial record and every approved gate before dependent product mutation. A stale digest, lock, temporary artifact with no valid record, validation failure, or filesystem error blocks progress. Preserve artifacts for inspection; never hand-delete recovery evidence to make a command pass.
+Omit `--expected-sha256` only for first creation; require an absent target. Commit the initial record and every approved gate before dependent product mutation. The exclusive lock serializes cooperating helper invocations; external mutation of its pathname is outside the contract. A stale digest, lock, temporary artifact with no valid record, validation failure, or filesystem error blocks progress. Preserve artifacts for inspection; never hand-delete recovery evidence to make a command pass.
 
 ## Assignment evidence
 

skills/develop/develop-workflow/scripts/checkpoint-record.mjs

@@ -38,7 +38,6 @@ const nodeIo = Object.freeze({
   open: (...args) => fs.open(...args),
   readFile: (...args) => fs.readFile(...args),
   rename: (...args) => fs.rename(...args),
-  stat: (...args) => fs.stat(...args),
   unlink: (...args) => fs.unlink(...args),
   randomUUID: () => randomUUID(),
 });
@@ -173,10 +172,6 @@ async function unlinkQuietly(io, path) {
   }
 }
 
-function sameFile(left, right) {
-  return left.dev === right.dev && left.ino === right.ino;
-}
-
 async function readExisting(io, target) {
   try {
     return { exists: true, bytes: await io.readFile(target) };
@@ -265,7 +260,6 @@ export async function checkpointRecord(request) {
   }
 
   let lockHandle = null;
-  let lockIdentity = null;
   let tempHandle = null;
   let tempPath = null;
   let primaryError;
@@ -273,14 +267,13 @@ export async function checkpointRecord(request) {
   try {
     try {
       lockHandle = await io.open(lock, "wx", FILE_MODE);
-      lockIdentity = await lockHandle.stat();
     } catch (error) {
       if (isAlreadyExists(error)) {
         throw new CheckpointError("LOCK_EXISTS", "checkpoint target is locked; refusing to recover or overwrite the lock", {
           cause: error,
         });
       }
-      throw new CheckpointError("LOCK_FAILED", `could not acquire and identify checkpoint lock: ${messageFor(error)}`, {
+      throw new CheckpointError("LOCK_FAILED", `could not acquire checkpoint lock: ${messageFor(error)}`, {
         cause: error,
       });
     }
@@ -376,18 +369,7 @@ export async function checkpointRecord(request) {
       cause: lockCloseError,
     });
   }
-  if (lockIdentity !== null) {
-    let currentLockIdentity;
-    try {
-      currentLockIdentity = await io.stat(lock);
-    } catch (error) {
-      if (!isMissing(error) && primaryError === undefined) {
-        primaryError = new CheckpointError("LOCK_CLEANUP_FAILED", `could not verify checkpoint lock ownership: ${messageFor(error)}`, {
-          cause: error,
-        });
-      }
-    }
-    if (currentLockIdentity !== undefined && sameFile(lockIdentity, currentLockIdentity)) {
+  if (lockHandle !== null) {
     const lockUnlinkError = await unlinkQuietly(io, lock);
     if (lockUnlinkError !== undefined && !isMissing(lockUnlinkError) && primaryError === undefined) {
       primaryError = new CheckpointError("LOCK_CLEANUP_FAILED", `could not remove checkpoint lock: ${messageFor(lockUnlinkError)}`, {
@@ -395,7 +377,6 @@ export async function checkpointRecord(request) {
       });
     }
   }
-  }
 
   if (primaryError !== undefined) throw primaryError;
   return result;

skills/develop/develop-workflow/tests/checkpoint-record.test.mjs

@@ -175,36 +175,6 @@ test("serializes concurrent updates with an exclusive per-target lock", async ()
   assert.equal(await exists(`${target}.lock`), false);
 });
 
-test("does not remove a lock pathname replaced before cleanup", async () => {
-  const directory = await temporaryDirectory();
-  const target = join(directory, "record.md");
-  const lock = `${target}.lock`;
-  const replacement = "replacement lock";
-  let replaced = false;
-  const io = {
-    ...defaultIo,
-    open: async (path, flags, mode) => {
-      const handle = await defaultIo.open(path, flags, mode);
-      if (path !== lock || flags !== "wx") return handle;
-      return {
-        stat: (...args) => handle.stat(...args),
-        close: async () => {
-          await handle.close();
-          await fs.unlink(lock);
-          await fs.writeFile(lock, replacement, { mode: 0o600 });
-          replaced = true;
-        },
-      };
-    },
-  };
-
-  await checkpointRecord({ target, input: record(), io });
-
-  assert.equal(replaced, true);
-  assert.equal(await fs.readFile(lock, "utf8"), replacement);
-  assert.equal(await fs.readFile(target, "utf8"), record());
-});
-
 test("fails closed on a pre-existing stale lock and leaves it for recovery", async () => {
   const directory = await temporaryDirectory();
   const target = join(directory, "record.md");