WRI-534 Add Antigravity CLI worker support

[fazpu]

Summary

Adds Google Antigravity CLI (agy) as a first-class built-in team-harness worker type. The new antigravity template runs workers through agy --print so they can execute as non-interactive subprocesses, matching the official Antigravity CLI positioning as a terminal-first agent surface and the local agy --help command surface.

Context

Linear: WRI-534 (TH - add Antigravity CLI support)

Docs reviewed:

• Antigravity CLI overview: https://antigravity.google/docs/cli-overview
• Installation/auth docs: https://antigravity.google/docs/cli-install
• Settings/CLI overrides docs: https://antigravity.google/docs/cli-settings

I also verified the installed local CLI (agy --version -> 1.0.0) and agy --help, which exposes:

• --print / --prompt / -p for non-interactive single-prompt execution
• --dangerously-skip-permissions for auto-approving tool permissions
• --print-timeout for print-mode wait control
• --conversation <id> for explicit conversation resume
• no model flag, so the built-in template intentionally sets model_flag = false

Implementation

• Adds antigravity to DEFAULT_AGENT_TEMPLATES with:
  • command = ["agy"]
  • shared_flags = ["--dangerously-skip-permissions", "--print", "--print-timeout", "60m"]
  • resume_flags = ["--conversation", "{session_id}"]
  • model_flag = None because the CLI does not expose a model override flag
  • deduplication for standalone --dangerously-skip-permissions and --print flags
• Updates generated global/local config samples so th init documents the new worker and includes antigravity in the commented allowlist.
• Marks Antigravity resume metadata as supported/preferred resume mode when a caller already has a conversation id. Automatic capture remains unset because print mode does not emit stream-json session events.
• Adds Antigravity display styling in the console agent panel/event output.
• Updates README, changelog, package metadata keywords/description, and tests.

Validation

Passed:

uv run pytest src/tests/test_registry.py src/tests/test_config.py src/tests/test_worker_sessions.py src/tests/test_agent_tools.py
uv run pytest -k 'not test_stream_token_bold_rendering and not test_stream_token_heading_rendering'
uv run ruff check src
uv run ruff format --check src
uv run pyright
git diff --check

Notes:

• uv run pytest without exclusions currently fails on two unrelated console ANSI-style assertions: test_stream_token_bold_rendering and test_stream_token_heading_rendering. The output text is rendered, but the expected bold ANSI escape sequence is absent in this local environment.
• uv run ruff check . also reports issues in pre-existing untracked .agents/skills/skill-creator/... files. This PR leaves those untracked files untouched and validates tracked source with ruff check src.

User-facing behavior

After this change, users with Antigravity CLI installed and authenticated can run workers with:

th repl --agents antigravity

or include it in config allowlists as antigravity.

Model overrides passed through spawn_agent(model=...) are intentionally ignored for this worker until Antigravity CLI exposes a stable model flag.

[fazpu]

Self-review completed. I rechecked the command construction, generated config round-trip behavior, resume metadata, docs, and validation notes. No blocking issues found.

On --print-timeout: I think it should stay in the default Antigravity template. agy --help shows print mode has a built-in 5-minute timeout; the other worker CLIs do not expose an equivalent default timeout in their harness invocation path. Team-harness workers are expected to run longer than 5 minutes for normal delegated implementation/research tasks, so --print-timeout 60m prevents Antigravity from ending the worker before team-harness can manage it.