2026.08.23 - DCP Reliability Troubleshooting - Phase 4: Message-ID Sanitization

[lanhhoang]

• Add two narrow, ordered rules to stripHallucinationsFromString that catch bounded DCP message-ID fragments before lone-tag cleanup runs: a suffix-or-pair rule (<dcp|dpc>-message-id (optional) + m\d{4,} + </dcp|dpc-message-id>) and an orphan-opening rule (<dcp|dpc>-message-id + m\d{4,} + word boundary). Recognizes both dcp and the observed dpc transposition; preserves m0001abc, prose after orphan references, and non-m#### payloads (src/messages/strip.ts).
• Add focused regressions covering the observed m0112</dpc-message-id> suffix, bounded suffixes and transposed pairs, orphan references, prose preservation, ambiguous payloads (discussion, m0001abc), and idempotence for malformed references (tests/strip.test.ts).
• Add a message_end handler regression that drives the registered boundary through the actual handler in src/index.ts (no duplicate mapText() case in tests/message-end.test.ts) (tests/index.test.ts).
• Replace the prior pipeline hallucination test with one that asserts the persisted m0112</dpc-message-id> suffix is sanitized before canonical injection, leaving exactly one <dcp-message-id> tag and the correct m0002 ref (tests/pipeline.test.ts).

Verified end-to-end with the previous committed changes via pnpm check (471/471 tests) on commit da6ebbcc2557e6e07372dafc87dc6e7fe57a68c9.