W23: close mailroom metadata and network validation tests

- Refresh agents STATUS to W22.6 and exclude mailroom from metadata scans
- Add mailroom dispatch checklist and defensive rules
- Register F-23.D-1 and tag network input validation defense-in-depth
- Update network plugin tests for header length limits
- Fix LSP test metadata and remove orphan anthropic_internal.hpp

Verification:
- cmake --build build --config Release: 0 error, 0 warning
- ctest --test-dir build --output-on-failure: 10/10 passed
- ctest --test-dir build -R dstalk_smoke_test --output-on-failure: passed
- python scripts/check_agents_metadata.py --strict: passed

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

agents/POSTMORTEM.md

@@ -162,6 +162,8 @@
 | R-LOADER-CONTINUE | PM-004 | 插件加载/初始化永不 fail-fast，单点故障不级联阻断 |
 | R-LOADER-RETVAL | PM-004 | `initialize_all` 返回值 >0 = 部分成功，调用方必须区分 |
 | R-NO-FORCE-PUSH | PM-005 | 子代理 prompt 必须禁止 `git push --force` / `--force-with-lease` |
+| R-MAIL-SCOPE | Mailroom v1 | 子代理不得读写超出自身 inbox 之外的他人邮箱内容，仅可投递新邮件 |
+| R-MAIL-NO-DELETE | Mailroom v1 | 接收者不可物理删除邮件，只能移到 `agents/mailroom/archive/W<n>/`；删除仅限 CEO |
 
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