## Problem
`describe` returned an empty tree after ~15 s whenever the screen had an
accessibility label containing U+2028 (LINE SEPARATOR) — e.g. any
Element/Matrix reply preview, or rich text pasted from the web. Nothing
was wrong on the device: ax-service answered in ~170 ms with a full,
valid tree.
The tool-server framed the ax-service socket with
`readline.createInterface`, which splits on the four ECMAScript line
terminators (`\n`, `\r`, **U+2028, U+2029**). JSON permits U+2028
unescaped inside a string and `NSJSONSerialization` emits it raw, so one
valid frame became three fragments, none parsed, each was dropped by
`catch { return }`, and the pending RPC waited out its 10 s timeout —
then the native-devtools fallback waited out its 5 s. On top of that,
the timeout was reported as *"this simulator was not booted through
argent … call boot-device with force=true"*, sending the agent to reboot
a healthy simulator.
Minimal repro (no device): `JSON.stringify({label:"a b"})+"\n"` through
`readline` → 2 lines, 0 parsed.
## Fix
- **`utils/ndjson-socket.ts`** (new): `attachNdjsonReader` frames on the
`\n` byte only (`0x0A` can never occur inside a multi-byte UTF-8
sequence, so this is exact) and reports every unparseable frame to
stderr instead of swallowing it.
- Wired into the three device-facing JSON sockets: `ax-service.ts`,
`native-devtools.ts`, `android-devtools-client.ts` (the Android helper's
`org.json` and the iOS dylib's `NSJSONSerialization` both emit U+2028
raw, so all three were exposed). The two remaining `readline` uses read
process **stdout** for readiness markers — no JSON, no user text — and
are left alone.
- **`describe/platforms/ios/index.ts`**: a throw from `axApi.describe()`
(timeout, RPC error) now carries the error message in the hint and uses
the resolved api's real `degraded` flag, instead of being reported as
the boot caveat. Separate commit so it can be reverted independently.
## Verification
- 6 new unit tests for the reader (U+2028/U+2029 in a string, chunk
split mid-multibyte char, several frames per chunk, CRLF/empty lines,
dropped-frame reporting, trailing frame on `end`) and 3 for the hint
(`describe-tool.test.ts`). Full tool-server suite: 4816 passed.
- Live A/B on iPhone 16 / iOS 18.5, Safari page with `<meta
charset=utf-8>` and a U+2028 inside a `<p>`:
- argent 0.22.1 (`main`): `describe` **12.6 s**, `source:
native-devtools`, web text missing, false "not booted through argent"
hint.
- This branch (`dist` against installed binaries): **50 ms**, `source:
ax-service`, label `"In reply to Dave Loving it so far"` present, no
hint, 0 dropped frames logged.
## Docs
No docs update needed — no tool, CLI, config or flow surface changes.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
https://claude.ai/code/session_01VwqqHRhfuHXbKr6LYskxhJ
filip131311