Review

Solid fix for the no_prompt delivery stall, and the multi-backend selector is validated cleanly at every boundary (MCP → HTTP → coordinator, with rejection before worktree creation) and well covered by tests. One thing to confirm before merge, plus a few minor notes.

Needs confirmation

antigravity sub-tasks probably never receive the <sub-task-mode> preamble.

In coordinator.ts, the preamble target file is chosen from agentCmd:

codex / opencode → AGENTS.md
gemini           → GEMINI.md
copilot          → .agent.md
else (Claude)    → .claude/settings.local.json

antigravity maps to the agy command, which matches none of those .includes(...) checks, so it falls into the Claude else branch and the preamble is written to .claude/settings.local.json. Antigravity is a Gemini-lineage CLI (auth dir ~/.gemini/antigravity-cli per pty.ts), so it almost certainly doesn't read Claude's settings file — and there's no arg-based delivery fallback, injection is purely file-based. Net effect: antigravity children likely don't get the sub-task-mode rules and never learn to call land_self.

Since the PR ships antigravity as a selectable backend (with a passing test asserting it spawns as agy), this leaves the feature partially non-functional for that one backend. If antigravity reads GEMINI.md, the fix is a one-liner — route agy alongside gemini:

} else if (agentCmd.includes('gemini') || agentCmd === 'agy') {

Could you confirm which context file agy actually reads? If it's none of these, it may be cleaner to drop antigravity from the selectable set until it's wired up.

Minor

• Selecting a backend replaces all coordinator base args (selectedAgentArgs becomes the backend's built-in default, []). Dropping --model opus when switching to a different backend is correct, but selecting the same backend as the coordinator (e.g. backend: "claude" under a claude --model opus coordinator) also silently drops the model flag. Worth either inheriting args when the selected backend matches the coordinator, or noting "specifying backend opts out of all coordinator arg inheritance" in the tool description.

• ensureSymlinkExcludes(worktreePath, [...createdSymlinks, '.claude']) writes to --git-common-dir's info/exclude, which is shared by the main working tree and every worktree (the sibling ensureSandboxExcludes docstring even calls it "shared"). So root-anchored /.claude also hides newly-created untracked .claude/ files in the main checkout and other worktrees, not just this sandbox. Intended for the placeholder files, but the reach is broader than the comment implies — a one-line note would help.

• Codex redraw pattern (?:^|\s|q)›[^\r\n›]*?gpt-[\w.-]+\s+\w+\s+·\s+~?\/ is a broad heuristic. It only avoids a false "ready" on a damaged working frame because the busy patterns are checked first — and those only scan the last 500 chars (AGENT_BLOCKER_TAIL_CHARS) while ready matching runs over 1000. If a redraw also mangles the esc to interrupt / Working( markers, a busy Codex could read as ready. Low risk given the fixture coverage, just a known watch-point.

• coordinator.test.ts hand-copies the production regex into its prompt-detect mock, so those tests can silently drift from prompt-detect.ts. The real regex is separately exercised against the new fixtures in prompt-detect.test.ts, so coverage exists — just a maintenance smell (pre-existing).

Nice

• New readiness patterns are tested against the real classifier via recorded frame fixtures, not just mocks.
• The normalizePreambleFileContent extraction + normalizing both sides of the landing diff is a clean fix for the spurious committed-AGENTS.md diffs.
• getAgentByBackend deep-copies args, avoiding mutation of the shared DEFAULT_AGENTS.

Overall: good to merge once the antigravity preamble routing is confirmed or fixed.