refactor(app-server-protocol): remove dead item/fileChange/outputDelta notification

[andrei-hasna]

Summary

Removes the deprecated item/fileChange/outputDelta server-notification compatibility surface (FileChangeOutputDeltaNotification). Both the type doc-comments and the app-server README state the server no longer emits this notification, and there is no emitter path anywhere in codex-rs (core / app-server / protocol). The only consumers were a protocol union arm, a no-op TUI handler stub, and a test-client opt-out entry — all dead.

Changes

• Drop FileChangeOutputDeltaNotification struct (app-server-protocol/src/protocol/v2/item.rs).
• Drop the FileChangeOutputDelta => "item/fileChange/outputDelta" registration (app-server-protocol/src/protocol/common.rs).
• Drop the TUI routing arm (tui/src/app/app_server_event_targets.rs) and the match arm plus the now-unused no-op on_patch_apply_output_delta handler stub (tui/src/chatwidget/protocol.rs, protocol_requests.rs).
• Remove the item/fileChange/outputDelta entry from NOTIFICATIONS_TO_OPT_OUT (app-server-test-client/src/lib.rs).
• Remove the retained-for-compatibility README bullet (app-server/README.md).
• Regenerate app-server schema/TypeScript artifacts (just write-app-server-schema): deletes the FileChangeOutputDeltaNotification schema/TS files and drops the arm from the ServerNotification union.

Compatibility decision

Full removal. It is a server->client notification the server never emits, so removing it only means an out-of-tree client would never receive something it already never receives — no request/response contract break.

Out of scope (intentional)

The vendored Python SDK bindings under sdk/python still reference FileChangeOutputDeltaNotification. They are generated from a pinned published runtime (openai-codex-cli-bin==0.137.0a4), decoupled from the local source tree, so regenerating them now would either be a no-op or force an unrelated runtime bump. They will regenerate naturally on the next SDK runtime bump to a release containing this removal.

Preserved

The live item/fileChange/patchUpdated streaming path is untouched. Its app-server tests pass: turn_start_streams_apply_patch_change_updates_v2 and turn_start_does_not_stream_apply_patch_change_updates_without_feature_v2.

Validation

• rg for removed symbols outside schema/: zero hits.
• just check-fast -p codex-app-server-protocol: ok
• just test-fast -p codex-app-server-protocol: 256/256 pass (schema fixtures match)
• just check-fast -p codex-tui: ok
• just fmt: clean
• app-server patchUpdated tests: 2/2 pass

Generated with Claude Code

[andrei-hasna]

[codewith] Repaired the PR branch to current main with only the intended protocol-removal commit: f01fec9. Local validation passed: fmt, app-server-protocol check/tests, TUI check, and the focused app-server apply-patch streaming tests.\n\nI am not merging yet because CI is failing in cargo-deny, run 28853835648 / job 85575391225, on RUSTSEC-2026-0204 for crossbeam-epoch. That blocker is unrelated to this PR's protocol-only diff and appears covered by #174 (fix(deps): bump crossbeam-epoch to 0.9.20).