feat(#707): secure Discord service ingress (#716)

docs/scratchpads/tess-m1-sec-004-discord-ingress.md

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+# Scratchpad — TESS-M1-SEC-004 Discord ingress
+
+- **Task / issue:** TESS-M1-SEC-004 / #707
+- **Branch:** `fix/tess-discord-ingress` from `origin/main` at `59e49cfd`
+- **Objective:** Authenticate the Discord plugin service at gateway ingress; enforce explicit guild/channel/user allowlists; attach Discord message and generated correlation IDs; reject replayed native message IDs.
+- **Scope:** `plugins/discord`, `apps/gateway`, and existing Discord admin/developer protocol docs.
+- **Budget:** Task estimate 28K; no explicit hard cap supplied.
+- **Assumptions:** The Discord plugin and gateway share an injected high-entropy `DISCORD_SERVICE_TOKEN`; a configured Discord plugin fails closed without it. Allowlist configuration is comma-separated Discord snowflakes. Discord native message ID is the replay key, with bounded in-memory retention pending the M2 durable inbox/idempotency work.
+
+## Plan
+
+1. Add failing tests covering ingress service authentication/signing, unlisted guild/channel/user rejection, correlation propagation, and replay rejection.
+2. Implement the signed Discord ingress envelope and allowlist validation in the plugin.
+3. Authenticate and validate the envelope at the gateway boundary, then enforce bounded replay protection before agent dispatch.
+4. Document the service-token and allowlist operations; run focused and baseline gates; obtain independent review.
+
+## Progress
+
+- 2026-07-12: Intake complete; PRD TESS-SEC-005, architecture, and threat model reviewed.
+- Added service-token Socket.IO authentication, HMAC-signed Discord envelopes, default-deny guild/channel/user allowlists, correlated message metadata, bounded replay rejection, and fail-fast configuration checks.
+- Code and security reviews completed. Code review findings on service persistence ownership, package-boundary tests, disconnected ingress observability, and chat payload validation were remediated; final independent code review approved.
+
+## Risks / blockers
+
+- Existing `main` has known unrelated Prettier debt; only changed files will be held format-clean. Durable replay persistence is intentionally out of scope for this M1 prerequisite and belongs to TESS-M2 durable inbox/idempotency work.
+
+## Verification evidence
+
+- Focused ingress suite: `pnpm --filter @mosaicstack/gateway test -- discord-ingress.security.spec.ts` — 7 passed.
+- Gateway suite: `pnpm --filter @mosaicstack/gateway test` — 513 passed, 11 skipped.
+- Plugin suite: `pnpm --filter @mosaicstack/discord-plugin test` — no tests, passed by configured `--passWithNoTests`.
+- `pnpm typecheck` — passed.
+- `pnpm lint` — passed.
+- `pnpm format:check` — fails only on the known pre-existing Tess documentation debt listed in the task dispatch; changed files pass targeted Prettier verification.
+- Codex security review — no findings; final Codex code review — approved.