ios: add persistent Sybil Agent room

Integrate the shared Agent room, durable outbox, cursor replay and read state on iPhone and iPad. Reuse message rendering with native messaging layout and expandable tool details.

Validated with 58 Xcode package tests, six Simulator UI scenarios, read-only production connectivity and independent review.

ios/README.md

@@ -13,6 +13,64 @@ cancels superseded requests, and leaves the current conversation open. Clear the
 field to return to recent items. Searches use word prefixes (for example, `plan`
 finds `planning`); if more than 100 items match, refine the query.
 
+## Sybil Agent
+
+The permanent **Sybil Agent** sidebar item opens the persistent room on both
+phone and iPad. It uses the configured Sybil API URL (including an explicit
+`/api` path) and token. The room stays subscribed while other chats are selected;
+foreground and network recovery replay from the last merged cursor. Shared unread
+counts include only public assistant replies and are acknowledged after the
+visible transcript reaches the bottom and its entrance animation finishes.
+
+Multiple messages can be queued while the Agent works. The local outbox is saved
+atomically under Application Support before submission and is scoped to the API
+base URL. An interrupted send stays on its original bubble with **Retry**, retaining
+its request ID and timestamp across relaunch. A canonical server echo confirms it
+even if the HTTP acknowledgement is lost. Tool cards expand to show input, result,
+and error details. Attachments and model selection belong to ordinary chats.
+
+Agent contracts remain in `../docs/api/rest.md` and
+`../docs/api/streaming-chat.md`; this client requires no backend deployment.
+
+### Agent regression and Simulator checks
+
+Run these commands from this worktree's `ios/` directory:
+
+```sh
+just build
+just test
+just run
+just screenshot build/agent-evidence/simulator.png
+```
+
+`just test` runs reducer, cursor, outbox, presentation, shared-read and lifecycle
+regressions along with the existing app tests through Xcode on iPhone 16e.
+For interactive UI coverage, start the local fixture (Python with `aiohttp`):
+
+```sh
+python3 Tests/Fixtures/agent_server.py
+```
+
+In a second terminal, run:
+
+```sh
+just generate
+xcodebuild test -scheme SybilAgentUI \
+  -destination 'platform=iOS Simulator,name=iPhone 16e,OS=latest' \
+  -parallel-testing-enabled NO \
+  -resultBundlePath build/agent-evidence/phone-ui.xcresult
+```
+
+The fixture binds only to `127.0.0.1:8799`, uses `fixture-token`, and never contacts
+external services. UI tests exercise the real REST/WebSocket client and retain
+screenshots in the result bundle. They cover queued submissions, uncertain
+admission/retry, tools, asynchronous replies, inactive sidebar unread counts,
+shared reads, reconnect/malformed replay, foreground recovery, long-history scroll
+anchors and multiline keyboard layout. The launch arguments select the fixture
+through ordinary API settings; no fixture mode is compiled into the application.
+Use a fresh result-bundle path for each run. Check the same UI on iPad and with
+Simulator Reduce Motion enabled before release.
+
 ## Quick Question on macOS
 
 While the Catalyst app is running, **Option+Space** toggles a floating Quick