test: keep Codecov coverage on real agent communication paths (#374)

* test: keep Codecov coverage on real agent communication paths

PR #369 was merged before the final Codecov coverage fix landed, so this follow-up carries only the incremental real-path tests needed on top of main. The tests exercise AgentSummary lifecycle branches, mailbox fail-closed behavior, UDS client connection failure through a real capability file, and UDS response-reader framing without mock.module, warning suppression, feature fallback, or production-code churn.

Constraint: PR #369 is already merged; this branch must contain only the incremental Codecov repair on top of latest main

Rejected: Reopen or keep pushing the merged PR branch | merged PR refs do not update and would leave Codecov stale

Rejected: Mock bun:bundle or hide warnings | would reintroduce cross-test pollution and pseudo coverage

Rejected: Keep unrelated SendMessageTool production diff | it created avoidable patch-coverage debt without improving the runtime path

Confidence: high

Scope-risk: narrow

Directive: Keep these coverage tests on real paths; do not replace them with output suppression or feature-flag mocks

Tested: bunx tsc --noEmit --pretty false

Tested: bun run lint

Tested: bun test src\utils\__tests__\teammateMailbox.test.ts

Tested: bun test src\services\AgentSummary\__tests__\agentSummary.test.ts src\services\AgentSummary\__tests__\summaryContext.test.ts src\utils\__tests__\teammateMailbox.test.ts src\utils\__tests__\udsMessaging.test.ts src\utils\__tests__\udsResponseReader.test.ts packages\builtin-tools\src\tools\SendMessageTool\__tests__\udsRecipientSanitization.test.ts

Tested: bun run test:all

Tested: bun test --coverage --coverage-reporter lcov --coverage-dir coverage

Tested: bun run build

Tested: bun run build:vite

Tested: bun audit

Tested: git diff --check

Tested: Claude simplify review GO (.omx/artifacts/claude-simplify-codecov-20260427-1521.md)

Tested: Claude security review GO (.omx/artifacts/claude-security-codecov-20260427-1522.md)

Not-tested: GitHub-hosted Codecov upload after this amended commit until PR checks rerun

* test: keep review assertions tied to real failure paths

CodeRabbit flagged three non-blocking but valid review gaps: platform-specific mailbox errno checks, brittle UDS connection-failure message assertions, and missing AgentSummary reschedule proof after fork errors. This keeps the fixes narrow by tightening the affected assertions and adding a structured UDS connection error for tests to assert behavior instead of prose.

Constraint: PR #374 is a review follow-up and must not hide warnings, skip tests, or merge the PR.

Rejected: Matching the UDS failure message literal | preserves the brittle coupling CodeRabbit flagged.

Rejected: Asserting only that mailbox writes throw | would allow unrelated pre-path failures to pass.

Confidence: high

Scope-risk: narrow

Directive: Keep UDS connection-failure tests on structured error data, not display wording.

Tested: bun test src/services/AgentSummary/__tests__/agentSummary.test.ts src/utils/__tests__/teammateMailbox.test.ts src/utils/__tests__/udsMessaging.test.ts

Tested: bunx tsc --noEmit --pretty false

Tested: bun run lint

Tested: bun run test:all

Tested: bun test --coverage --coverage-reporter lcov --coverage-dir coverage

Tested: bun run build

Tested: bun run build:vite

Not-tested: GitHub-hosted CodeRabbit refresh until pushed.

* test: remove brittle review follow-up assumptions

CodeRabbit's second pass found two valid brittleness issues and one suggested callback-reference assertion that would not match production behavior. This keeps the production behavior unchanged: timers still schedule the summarizer closure, tests now assert timer-handle identity, and UDS connection errors use native Error.cause instead of shadowing it.

Constraint: Do not manufacture behavior just to satisfy a review hint; assertions must match the real AgentSummary scheduling contract.

Rejected: Assert a fresh scheduled callback function | scheduleNext intentionally passes the same runSummary closure each time.

Rejected: Store a custom cause field on UdsPeerConnectionError | native Error.cause is available under ESNext/Bun.

Confidence: high

Scope-risk: narrow

Directive: Timer tests should assert returned handle identity for ownership, not incidental numeric values.

Tested: bun test src/services/AgentSummary/__tests__/agentSummary.test.ts src/utils/__tests__/udsMessaging.test.ts

Tested: bunx tsc --noEmit --pretty false

Tested: bun run lint

Tested: bun run test:all

Tested: bun test --coverage --coverage-reporter lcov --coverage-dir coverage

Tested: bun run build

Tested: bun run build:vite

Not-tested: GitHub-hosted CodeRabbit refresh until pushed.

* test: enforce structured UDS timeout failures

CodeRabbit's follow-up surfaced a real consistency gap: UDS send socket errors used UdsPeerConnectionError while response timeouts still rejected a generic Error. Timeouts now use the same structured peer failure contract, and the test exercises that path through a short explicit timeout instead of waiting for the production default.

The AgentSummary unchanged-fingerprint test now also asserts that the second unchanged tick does not log errors, preserving the existing behavior checks without changing production scheduling semantics.

Constraint: Keep the production timeout default at 5000ms while allowing tests to exercise the timeout path quickly.

Rejected: Leave timeout failures as generic Error | callers would need separate handling for the same peer connection failure class.

Confidence: high

Scope-risk: narrow

Directive: Keep UDS send timeout and socket-error branches on the same structured error contract.

Tested: bun test src/services/AgentSummary/__tests__/agentSummary.test.ts src/utils/__tests__/udsMessaging.test.ts

Tested: bunx tsc --noEmit --pretty false

Tested: bun run lint

Tested: bun run test:all

Tested: bun test --coverage --coverage-reporter lcov --coverage-dir coverage

Tested: bun run build

Tested: bun run build:vite

Not-tested: GitHub-hosted CodeRabbit refresh until pushed.

---------

Co-authored-by: unraid <local@unraid.local>

src/utils/__tests__/teammateMailbox.test.ts

@@ -1,9 +1,10 @@
 import { afterEach, beforeEach, describe, expect, test } from 'bun:test'
-import { mkdir, readFile, rm, writeFile } from 'node:fs/promises'
+import { mkdir, readFile, rm, stat, writeFile } from 'node:fs/promises'
 import { mkdtempSync } from 'node:fs'
 import { tmpdir } from 'node:os'
 import { dirname, join } from 'node:path'
 import type { Message } from 'src/types/message.js'
+import { getErrnoCode } from 'src/utils/errors.js'
 import {
   compactMailboxMessages,
   getLastPeerDmSummary,
@@ -171,6 +172,17 @@ describe('compactMailboxMessages', () => {
 
     expect(compacted).toEqual([])
   })
+
+  test('returns an empty mailbox when all retention lanes are disabled', () => {
+    const compacted = compactMailboxMessages([message('unread', false)], {
+      maxMessages: 0,
+      maxReadMessages: 0,
+      maxUnreadProtocolMessages: 0,
+      maxRetainedBytes: 1_000,
+    })
+
+    expect(compacted).toEqual([])
+  })
 })
 
 describe('teammate mailbox retention', () => {
@@ -331,6 +343,32 @@ describe('teammate mailbox retention', () => {
     expect(await readFile(inboxPath, 'utf-8')).toBe('{not-json')
   })
 
+  test('writeToMailbox rejects when the inbox path is already a directory', async () => {
+    const inboxPath = getInboxPath('worker', 'alpha')
+    await mkdir(inboxPath, { recursive: true })
+
+    const error = await writeToMailbox(
+      'worker',
+      {
+        from: 'team-lead',
+        text: 'new',
+        timestamp: new Date(5).toISOString(),
+      },
+      'alpha',
+    ).then(
+      () => undefined,
+      err => err,
+    )
+
+    const code = getErrnoCode(error)
+    expect(code).toBeDefined()
+    if (code === undefined) {
+      throw new Error('Expected filesystem errno code')
+    }
+    expect(['EISDIR', 'EPERM', 'EACCES']).toContain(code)
+    expect((await stat(inboxPath)).isDirectory()).toBe(true)
+  })
+
   test('readMailbox fails closed on corrupt mailbox content', async () => {
     const inboxPath = getInboxPath('worker', 'alpha')
     await mkdir(dirname(inboxPath), { recursive: true })