Sync upstream 2fbd4318fc (stage 2: React Compiler rollout)

[henrychu04]

Stage 2 of catching up to upstream 4b1024d: merges upstream through 2fbd431 (322 commits after 33aa461).

Upstream brought

• The React Compiler now covers every web file, with manual memoization and "use memo" removed.
• Web DOM tests moved to a headless-Chromium browser Vitest project.
• KnownWorkspaces and write-target hardening (refactor(server): resolve project and worktree folders in one place pingdotgg/t3code#20449): unknown cwds are rejected, and nothing is written into git folders.
• Pull request diff-file reads are limited to files in the change request.
• -- ends option parsing for CLI arguments (refactor(server): route git config through one env helper and end option parsing before names pingdotgg/t3code#20440).
• Background subagents keep T3 tools after the parent turn ends (fix(server): background subagents keep T3 tools after the parent turn ends pingdotgg/t3code#19751); subagent work cut by a restart wakes its thread (fix(server): wake threads whose subagents' background work a restart cut pingdotgg/t3code#19750).
• Fixes for a sidebar crash, settings search, and the agents pill.

Fork adaptations

• Files upstream rewrote for the compiler were rebuilt from upstream with the fork's delta replayed. Fork-heavy files keep the fork's version plus the upstream hunks that applied whole; upstream's changes to them were compiler-only.
• WorkspaceFileSystem keeps the revision-checked edits and create-only files, and adds upstream's KnownWorkspaces check and git-folder refusal to both write paths. Upstream's write-target tests are ported.
• GitLab: the numeric MR selector's --repo now goes before upstream's --.
• useFileSaveCoordinator uses upstream's structure, with the fork's revision tracking written so the compiler accepts it.
• The browser test project is carried and run, as you decided. reactCompilerCoverage skips four fork-only files the compiler bails on.
• Cut: the desktop update, WSL/SSH/local-backend, preview, usage, OpenCode, and Antigravity pieces upstream touched, plus upstream's credential-migration test.

Verification

• Passed: every pnpm test:coder suite, including about 6,250 web tests across the unit and browser projects, except the known serverSettings symlink-watcher flake (it passes when run alone).
• Passed: all typechecks, knip, pnpm build, and vp fmt --check on the changed files.
• Section 5 checks: no Claude transport or SDK changes and no new RPCs; contract changes are upstream's own.
• Section 6 checks: fork-delta and upstream-addition lists reviewed; every remaining difference is a listed cut or a memoization restructure.
• No live Coder smoke run.

🤖 Generated with Claude Code