feat(comms): P1 presence — minimal Synapse + fleet presence room + mosaic.presence heartbeat + liveness

Implements RFC-001 P1 (the first shippable slice): deterministic Matrix
presence/liveness on a single-instance dev Synapse.

- infra/matrix/: DEV Synapse (RFC-002 Mode B, federation OFF, self-signed TLS,
  enable_registration:false, appservice registration wired). Rendered from
  parameterized templates — zero hardcoded topology. .data is gitignored.
- packages/comms/: minimal MACP presence SDK — set presence, run the
  mosaic.presence heartbeat (seq + interval per RFC-001 §4.5), and a
  deterministic liveness reader (online/away/offline from heartbeat age, NOT
  native-presence-timeout). Liveness core written RED-FIRST. 19 vitest tests.
- tools/matrix-presence-harness/: minimal provisioner (registers >=3 agent
  MXIDs, creates the fleet presence room, joins them — reuses the existing
  @mosaicstack/appservice intent lib) + an E2E validation harness proving
  A2/A3/A4 against a real Synapse.
- eslint.config.mjs: register packages/comms/vitest.config.ts with the
  type-aware project service (same as other packages' vitest configs).

DEV-compose validated only; production deploy is a separate coordinated step
(deploy-holds respected).

Part of the comms-evolution program (RFC-001 P1)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0158NZqN2n2ymKFeJAZ4GUCb

infra/matrix/README.md

@@ -0,0 +1,53 @@
+# infra/matrix — DEV Synapse for RFC-001 P1 (presence)
+
+> **DEV-ONLY. LOCAL SANDBOX.** This stack is for local presence validation. It
+> must **never** be pointed at, or run alongside, a live/production homeserver.
+> It is single-instance, federation-OFF, self-signed TLS — the smallest slice
+> RFC-002 §9 says P1 needs (Mode B single-domain, no federation, no IP-only, no
+> secret-rotation story).
+
+## What this is
+
+A single Synapse homeserver rendered from committed **templates** (no hardcoded
+topology — RFC-002 G2). Every topology fact is an environment variable with a
+dev default:
+
+| Var                  | Default            | Meaning                                             |
+| -------------------- | ------------------ | --------------------------------------------------- |
+| `MATRIX_SERVER_NAME` | `matrix.localhost` | Synapse `server_name` (the `:suffix` of every MXID) |
+| `MOSAIC_AS_ID`       | `mosaic-as`        | appservice id / registration filename               |
+| `MATRIX_HTTP_PORT`   | `18008`            | host port → Synapse 8008 (plain HTTP)               |
+| `MATRIX_TLS_PORT`    | `18448`            | host port → Synapse 8448 (self-signed TLS)          |
+
+Secrets (`as_token`, `hs_token`, Synapse macaroon/form/registration secrets)
+are **throwaway values generated at bring-up** into `.data/dev-secrets.env`
+(gitignored). In production these are crown-jewel secrets held by the
+SecretBackend (RFC-001 §8 / RFC-002 §4) — never committed.
+
+## Files
+
+- `docker-compose.dev.yml` — Synapse (+ optional Element under `--profile element`).
+- `synapse/homeserver.dev.yaml.tpl` — rendered Synapse config (Mode B, `enable_registration: false`, appservice wired, native TLS).
+- `synapse/log.config` — Synapse logging.
+- `appservice/mosaic-as.dev.yaml.tpl` — minimal AS registration (declares the `@agent-*` user namespace).
+- `dev-up.sh` / `dev-down.sh` — bring up / tear down (`--purge` wipes `.data`).
+- `.data/` — **gitignored** runtime state (rendered config, sqlite db, signing key, self-signed certs, dev secrets).
+
+## Usage
+
+```bash
+./dev-up.sh                       # render config, gen signing key + TLS cert, boot Synapse
+# ... run the validation harness (tools/matrix-presence-harness/run.sh) ...
+./dev-down.sh            # stop, keep .data
+./dev-down.sh --purge   # stop and wipe .data for a pristine next boot
+
+# optional human view (A4) — Element pointed at the dev server:
+docker compose -f docker-compose.dev.yml --profile element up -d element
+#   -> http://127.0.0.1:18080
+```
+
+## Acceptance evidence (A1)
+
+- TLS (self-signed) reachable: `curl -sk https://127.0.0.1:18448/_matrix/client/versions` → `200`.
+- Open registration OFF: `POST /_matrix/client/v3/register` → `M_FORBIDDEN "Registration has been disabled"`.
+- AS-token registration bypasses the flag by design (that is how agents are provisioned).