feat(presence): typed awareness on the presence frame (lync 0.4.0)

[deepfates]

What

Builds the LIVE-SHARED awareness half of the loom on lync's existing ephemeral presence frame, per the pinned presence contract. lync's durable loss-free sync was already proven; this adds who is here right now, where their attention is, and are they typing — without ever persisting it.

The relay stays a stateless fanout — relay.ts is untouched. Nothing presence-related is written to disk.

Contract (pinned)

LyncPresence carried ONLY on the {t:"presence"} frame, NEVER stored:

{ clock: number,                 // monotonic uint per client; apply iff strictly greater (LWW per participant)
  state: null | {                // null == graceful leave -> remove immediately
    actor: string,               // same string as durable turn authorship
    via?: string, focus?: string | null, typing?: boolean } }

The frame also carries a per-connection client id — the LWW key, distinct from actor (one human may run several clients). This is the seam a co-author (textile) builds to; it is pinned by test/presence-schema-lock.test.ts.

Changes

• sync-protocol: typed LyncPresence + client on PresenceFrame; decodeFrame validates and canonicalizes (drops unknown extras, rejects non-integer/negative clocks) so a bad payload never poisons the awareness clock.
• presence-awareness (new module): client-side per-participant state machine — apply-iff-clock-strictly-greater (no CRDT merge), heard-from lastSeen refresh, ~15s self-rebroadcast heartbeat, ~30s TTL local removal, state=null immediate leave, {added,updated,removed} callback keyed by clientId, and real-timer start()/stop().
• synced-store: onPresence / presence() now carry (root, client, LyncPresence).

Tests (retire the untested-primitive gap — only a codec roundtrip existed before)

• presence-schema-lock — pins the exact wire shape.
• presence-awareness unit — LWW, immediate leave, TTL sweep, heartbeat liveness + TTL-recovery, and start()/stop() over fake-clocked real timers.
• presence-awareness.integration — real relay + two real synced stores: typed presence A→B, silent-A TTL removal, null-leave immediate removal, and an assertion the relay wrote nothing to disk (readdir before == after; no <root>.lync).

Full suite: 123 passed (111 baseline + 12 new).

Version 0.3.0 → 0.4.0 (additive minor). Not published (owner's 2FA). Do not merge.