feat(app): restore recent chat while reconnecting (#2206)

Keep a small non-authoritative view of the last focused chat so the app can paint it before the daemon finishes revalidation. Bound persistence to one focused agent per host and evict whole host entries to limit storage and serialization work.

docs/architecture.md

@@ -99,12 +99,20 @@ Cross-platform React Native app that connects to one or more daemons.
 
 - Expo Router navigation (`/h/[serverId]/workspace/[workspaceId]`, `/h/[serverId]/agent/[agentId]`, etc.). The `workspaceId` URL segment is an opaque workspace id, not a directly meaningful filesystem path.
 - `HostRuntimeController` manages saved host connections, reconnection, and per-host runtime state
+- `runtime/replica-cache` keeps a non-authoritative per-host display replica in AsyncStorage: only the last focused agent, its workspace, and a short timeline tail. It restores before navigation becomes ready, leaves remote hydration flags false, and is atomically replaced by the normal snapshot-plus-delta synchronization path.
 - `SessionContext` wraps the daemon client for the active session
 - Composer UI and submit/draft behavior live in `packages/app/src/composer/`; screens and panels should integrate it from there instead of dropping composer internals into `components/`, `hooks/`, or `screens/workspace/`
 - Timeline reducers in `timeline/session-stream-reducers.ts` handle compaction, gap detection, sequence-based deduplication
 - Timeline sync correctness is documented in [docs/timeline-sync.md](timeline-sync.md): live streams are for immediacy, `fetch_agent_timeline_request` is authoritative, and catch-up is paged but complete.
 - Voice features: dictation (STT) and voice agent (realtime)
 
+The replica cache exists only to paint stale data immediately while the host connects. It does not
+own mutations, infer deletions, or replace daemon reconciliation. Pending permission requests are
+not restored from it. AsyncStorage is not encrypted, so the cached timeline tail may contain source
+code, prompts, and tool output; encrypted-at-rest storage is a separate product/security decision.
+Its serialized payload has a 1 MiB byte budget and evicts whole host snapshots in least-recently-
+written order; a single oversized host is omitted rather than partially restored.
+
 ### `packages/cli` — Command-line client
 
 Commander.js CLI with Docker-style commands. Common agent operations are also exposed at the top level (e.g. `paseo ls`, `paseo run`).