fix(matrix-bridge): sweep all 8 deferred audit findings

[replicas-connector]

Summary

Closes out every deferred-with-rationale item from the three audit rounds tonight (commit 2313473, PR #18, PR #19). All 8 now have a real code fix.

Round 1 (correctness/lifecycle) — 4 items

#1. pending-decrypt:* prune cron — listener alarm now runs a 30-min periodic prune that drops queue entries older than 7 days and deletes empty queues. Bounds long-term DO storage growth from sessions whose forwarders went offline before responding.

#2. seen:* KV race redesign — dispatch dedupe was using KV's eventual read-modify-write, letting two concurrent reads both see "absent" and both proceed. New /dedup-claim endpoint on MatrixListener wraps the check + write in blockConcurrencyWhile for genuine put-if-absent semantics. Periodic prune handles cleanup (1h TTL); KV fallback preserved if the listener DO is unreachable.

#3. /admin/listener/reload-keys endpoint — clears the in-memory cachedKeys + cachedCurve25519 so the operator can rotate Megolm session keys (MATRIX_MEGOLM_KEYS_JSON) without a full redeploy.

#4. parsePlan hijack tightening — only accept Plan(d/t) headers BEFORE any tool calls and before any prior plan has been parsed. Prevents a confused/adversarial agent from overwriting in-progress view by emitting Plan (5/5) mid-turn to fake completion.

Round 2 (security/spec/integration) — 4 items

#5. m.forwarded_room_key validation — vault now tags captured Megolm keys as forwarded vs live; listener checks key-request:* prefix to confirm we previously asked for the (room, session). If not, calls new vault /keystore-delete to evict the unsolicited key. Closes the "any Olm-paired sender can plant Megolm keys for any room" hole.

#6. usage:org KV race — routed through OlmVault singleton DO via new /usage-bump (atomic write) and /usage-read (read) endpoints. Concurrent Done frames across rooms can no longer drop entries via read-modify-write race.

#7. Olm session cap bump — was .slice(-8), now .slice(-32). Verified multi-device senders rotate fast enough that 8 was occasionally dropping legitimate live sessions. Evictions are now logged so the operator can spot pathological churn.

#8. /admin/recover-room missing-senderKey warning — surface bridges that strip the outer sender_key field (m.room_key_request routing degrades to * when missing, may not land on the originating device).

Validation

• npm run typecheck ✅
• npm test ✅ 102/102 tests pass
• Deployed (94631766-f1ea-4535-af48-1ac6a72b1ab2)

Rolling tally tonight: 19 findings · 19 shipped · 0 deferred.

Test plan

• Typecheck clean
• All tests pass
• Deploy succeeds
• After merge: confirm /admin/listener/reload-keys clears in-memory caches
• After merge: confirm normal dispatch path still works (DO RPC adds ~10ms)
• Watch tail for [olm-vault] evicted unsolicited forwarded key — any hits warrant investigation of the forwarding device

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_{Created by Jaden (jadengarza@pm.me) with Replicas
Workspace  ·  Slack Thread}

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