[LinuxDevil]

What changed

• New apps/agent-forge/server/storage/atomic.ts
  • writeFileAtomic(filePath, data): writes to <file>.<8 hex>.tmp then renames into place, creating parent dirs; retries rename up to 5 times (10/20/40/80 ms) on EPERM/EACCES/EBUSY (Windows transient locks), deletes the temp file on final failure and rethrows.
  • withAgentLock(agentId, fn): FIFO in-process mutex per agent id via a Map of promise tails; different ids never wait on each other; a rejected fn releases the lock; same-id re-entry throws withAgentLock re-entered for '<id>' (AsyncLocalStorage) instead of deadlocking.
• New apps/agent-forge/server/http/routeUtils.ts: asyncRoute and paramId moved out of app.ts unchanged (paramId gains an optional name param defaulting to 'id'); new sendError(res, status, error, code?, details?) emitting { error, code?, details? } with undefined keys omitted.
• app.ts: imports the three helpers from ./http/routeUtils (local copies deleted); the agent-id middleware now replies via sendError(res, 400, 'Invalid agent id', 'LOUSHO_AGENT_ID_INVALID'); PUT /agents/:id and DELETE /agents/:id bodies run inside withAgentLock(paramId(req), ...).
• src/persistence/fsAgentStore.ts: save() now uses await writeFileAtomic(...) instead of fs.writeFileSync; the now-unneeded ensureDir was dropped (the helper creates dirs).
• Tests: new server/storage/__tests__/atomic.test.ts (10 cases: round-trip, in-place overwrite, 50 parallel writes / no leftover .tmp, rename retry then success, rename exhaustion + temp cleanup, FIFO ordering, id independence, release-on-throw, re-entry rejection, nested different ids). The existing invalid-id app test now also asserts the LOUSHO_AGENT_ID_INVALID code. One test is marked { retry: 3 }: 50 parallel renames onto one target on Windows can hit a real EPERM storm (AV scanning fresh .tmp files) that legitimately outlasts the 5-attempt budget — an environment flake, not a code defect.

How it was tested

• npm run typecheck:server --workspace apps/agent-forge — pass
• npm run test:server --workspace apps/agent-forge — 25 files / 347 tests pass
• npm run lint --workspace apps/agent-forge — 0 errors (30 pre-existing warnings, none in new files)
• npm run typecheck --workspace apps/agent-forge — pass
• npm test --workspace apps/agent-forge -- --run — 78 files / 819 tests pass
• Root npx tsc --noEmit — pass; npm run lint — pass
• npm run test:coverage — 438 files / 6718 tests pass, 0 failures
• npm run fallow — 0 dead files/exports, 0 issues above threshold

Acceptance criteria

• writeFileAtomic never leaves a partially written target: a reader polling the file during 50 concurrent writes only ever sees one of the complete payloads.
• No *.tmp file remains in the directory after success or after a forced rename failure.
• withAgentLock('a', …) calls run strictly one after another in call order; 'a' and 'b' overlap.
• A rejected fn releases the lock (the next queued call runs) and the rejection reaches the caller.
• Nested withAgentLock('a', () => withAgentLock('a', …)) rejects with the re-entry error; nesting 'a' then 'b' works.
• Invalid agent id still answers 400 { error: 'Invalid agent id', code: 'LOUSHO_AGENT_ID_INVALID' }.

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