[johoja12]

Part 1 of the review split requested in #769. This changes the existing Notifications-mode transport only: authorized inbound message IDs are durably claimed before terminal/attachment writes, partial input is never blindly replayed, and full-text output parts record their payload fingerprints and confirmed message IDs separately. Retries skip confirmed parts and stop on uncertainty. Unversioned identical automatic notices also pause after uncertain delivery; deliberate notices remain distinct requests.

REST retries use one enforced nonce, preserve multipart payloads, respect the real retry-after and do not retry ambiguous thread creation. The journal is bounded to 2048 metadata records/2 MB with seven-day retention and private atomic writes. It contains no prompt/response/file bytes or token. Invalid journals fail closed. Acceptance is transport acceptance, never fabricated task completion.

Scope excludes Full-mode channels/threads and transcript readers, questions and model controls, Activity/history/Results, generated files and remote uploads. Those remain in the draft integration reference #769 and will be reviewed separately.

Validation: 116 delivery and existing bridge tests pass, including duplicate/restarted inbound events, partial input, persistent-store refusal, refused/uncertain multipart output, formatter changes, nonce reuse, retry limits and scope cancellation. Typecheck, lint and format checks pass. Isolated curl /api/status and /api/discord return success with Discord disabled; the temporary instance was stopped. No production deployment or diagnostic Discord messages.

Tracking: johoja12#218 (parent johoja12#97).