code-quality batch (T-112)

Seven small consultant findings, one commit:

1. TreeSitterLib stores last dlopen error + path in static fields
   instead of swallowing them. Callers that observe a null instance
   can now read the diagnostic.

2. Drop the Cmsghdr alias in libc.dart — back-compat shim with no
   callers; CLAUDE.md forbids those in a solo repo.

3. Drop EditorController._events field + the unused_field
   suppression. The constructor still subscribes via `events.on<...>`
   for _eventSub; the field itself was speculative retention.

4. Replace inline hex / errno literals in native_pty.dart with
   PosixErrno.{eintr,ebadf,epipe} and new libc.{pollin, pollAnyErr,
   sighup, sigkill, sigwinch}. PosixErrno gains eintr.

5. ExtensionManager records activate/deactivate exceptions in a
   `_failed` map exposed as `failedExtensions` + `didFail(id)`.
   Listeners are notified on entry/exit; cleared on a clean
   activate. UI surfaces the degraded state instead of pretending
   everything is fine.

6. file_tree_view imports FileEntry via the clide.dart barrel
   instead of `package:clide/src/files/listing.dart` directly — the
   leak the consultant flagged (barrel already re-exports it).

7. test_app branch in main.dart wrapped in `if (kDebugMode)` so
   release tree-shaker elides the test harness from shipping
   binaries. Source import stays; tree-shake handles the rest.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.pql/changelog/ticket_history/2026-05.sql

@@ -1803,3 +1803,5 @@ INSERT INTO ticket_history (ticket_id, field, old_value, new_value, changed_by,
 INSERT INTO ticket_history (ticket_id, field, old_value, new_value, changed_by, changed_at, created_at, updated_at, deleted_at, hash, canonical_version) VALUES ('T-105', 'status', 'in_progress', 'done', NULL, '2026-05-17 19:56:28', '2026-05-17 19:56:28', '2026-05-17 19:56:28', NULL, '62dfdadc31b2c231afd837fb46f0a114', 1) ON CONFLICT(hash) DO NOTHING;
 INSERT INTO ticket_history (ticket_id, field, old_value, new_value, changed_by, changed_at, created_at, updated_at, deleted_at, hash, canonical_version) VALUES ('T-108', 'status', 'backlog', 'in_progress', NULL, '2026-05-17 19:58:13', '2026-05-17 19:58:13', '2026-05-17 19:58:13', NULL, 'a5dbfe5881e152e82538181b0fe56609', 1) ON CONFLICT(hash) DO NOTHING;
 INSERT INTO ticket_history (ticket_id, field, old_value, new_value, changed_by, changed_at, created_at, updated_at, deleted_at, hash, canonical_version) VALUES ('T-108', 'status', 'in_progress', 'done', NULL, '2026-05-17 20:05:38', '2026-05-17 20:05:38', '2026-05-17 20:05:38', NULL, '6815472fbfaa6d7740945b42d4c87f57', 1) ON CONFLICT(hash) DO NOTHING;
+INSERT INTO ticket_history (ticket_id, field, old_value, new_value, changed_by, changed_at, created_at, updated_at, deleted_at, hash, canonical_version) VALUES ('T-112', 'status', 'backlog', 'in_progress', NULL, '2026-05-17 20:06:30', '2026-05-17 20:06:30', '2026-05-17 20:06:30', NULL, '52271781bf987a984d9f219956034d1f', 1) ON CONFLICT(hash) DO NOTHING;
+INSERT INTO ticket_history (ticket_id, field, old_value, new_value, changed_by, changed_at, created_at, updated_at, deleted_at, hash, canonical_version) VALUES ('T-112', 'status', 'in_progress', 'done', NULL, '2026-05-17 20:11:16', '2026-05-17 20:11:16', '2026-05-17 20:11:16', NULL, '6d51964a3ad7f1948f54a7c769336841', 1) ON CONFLICT(hash) DO NOTHING;

.pql/changelog/tickets/2026-05.sql

@@ -1788,3 +1788,14 @@ INSERT INTO tickets (id, type, parent_id, title, description, status, priority,
 2. Replace swallowed `onTimeout: () {}` with `onTimeout: () => fail(''...'')`.
 
 Source: consultants.md "Tests — Findings — [Major]".', 'done', 'medium', NULL, NULL, NULL, '2026-05-17 18:47:59', '2026-05-17 20:05:38', NULL, '33e15d84caed686e88fc42f1f4a3586c', 1) ON CONFLICT(id) DO UPDATE SET type=excluded.type, parent_id=excluded.parent_id, title=excluded.title, description=excluded.description, status=excluded.status, priority=excluded.priority, assigned_to=excluded.assigned_to, team=excluded.team, decision_ref=excluded.decision_ref, updated_at=excluded.updated_at, deleted_at=excluded.deleted_at, hash=excluded.hash, canonical_version=excluded.canonical_version WHERE excluded.updated_at > tickets.updated_at OR (excluded.updated_at = tickets.updated_at AND excluded.hash > tickets.hash);
+INSERT INTO tickets (id, type, parent_id, title, description, status, priority, assigned_to, team, decision_ref, created_at, updated_at, deleted_at, hash, canonical_version) VALUES ('T-112', 'task', 'T-97', 'quick-wins: code-quality cleanups', 'Batch of small consultant findings that share a domain (code quality):
+
+1. Replace silent `catch (_)` in `tree_sitter_ffi.dart:197,206` with a logged last-error — `DynamicLibrary.open` failures are currently discarded.
+2. Delete `Cmsghdr` alias in `libc.dart:201-202` ("backward compatibility" — CLAUDE.md forbids in a solo repo).
+3. Remove `// ignore: unused_field` in `editor_controller.dart:25` (speculative retention; fix not silence).
+4. Consume `libc.dart` constants / `PosixErrno` in `native_pty.dart` instead of inline hex (`0x0001`, `28`, `4`, `9`).
+5. `ExtensionManager.activate` (`extensions_manager.dart:141-143`) swallows exceptions — surface a "degraded" state for the UI.
+6. Verify `file_tree_view.dart:8` barrel leak (commit `5cad982` may already cover this).
+7. Move `test_app.dart` out of production `main.dart` import graph (gate behind separate entrypoint or `kDebugMode`).
+
+Source: consultants.md (Code Quality + Architecture Findings — Minor).', 'done', 'low', NULL, NULL, NULL, '2026-05-17 18:48:20', '2026-05-17 20:11:16', NULL, 'fccc783ff24be83f6d5a498e936c4af9', 1) ON CONFLICT(id) DO UPDATE SET type=excluded.type, parent_id=excluded.parent_id, title=excluded.title, description=excluded.description, status=excluded.status, priority=excluded.priority, assigned_to=excluded.assigned_to, team=excluded.team, decision_ref=excluded.decision_ref, updated_at=excluded.updated_at, deleted_at=excluded.deleted_at, hash=excluded.hash, canonical_version=excluded.canonical_version WHERE excluded.updated_at > tickets.updated_at OR (excluded.updated_at = tickets.updated_at AND excluded.hash > tickets.hash);