Update google-antigravity from SDK evolution report

[ebarti]

SDK Evolution PR

This PR updates the google-antigravity lock from 0.1.2 to 0.1.4 and hardens the local SDK evolution agent so SDK update candidates always receive candidate-version API snapshot diffs before implementation can be considered safe.

Agent-Generated Evidence

The committed proof report was generated through agent-runtime-kit using the real antigravity-agent-sdk runtime from a temporary pre-update checkout where the lockfile still had google-antigravity 0.1.2:

env -u UV_EXCLUDE_NEWER uv run python -m examples.sdk_evolution_agent \
  --runtime antigravity-agent-sdk \
  --package google-antigravity \
  --refresh-preview \
  --report-dir /tmp/ark-sdk-evolution-proof-with-diffs

Committed report:

reports/sdk-evolution-proof/20260622T085528Z/report.md

Key proof artifacts:

• reports/sdk-evolution-proof/20260622T085528Z/config.json records runtime: antigravity-agent-sdk and inspect_candidates: true.
• reports/sdk-evolution-proof/20260622T085528Z/evidence.json records Update google-antigravity v0.1.2 -> v0.1.4 from uv lock --dry-run -P google-antigravity with freshness cutoffs removed.
• reports/sdk-evolution-proof/20260622T085528Z/api_diffs.json contains the candidate API diff from 0.1.2 to 0.1.4, including added, removed, and changed symbols.
• reports/sdk-evolution-proof/20260622T085528Z/api_snapshots/ contains both the current and candidate API snapshots.

Implementation

• Updated uv.lock to google-antigravity 0.1.4.
• Made candidate API inspection mandatory for SDK update candidates, including programmatic RunOptions calls.
• Switched candidate comparison to the lockfile baseline first, so a locally synced environment cannot hide a stale lockfile.
• Added an implementation guard that blocks SDK updates when uv lock --dry-run reports an update but api_diffs.json lacks a candidate diff object for that package.
• Added a manual-design gate so manual_design_required=true always makes safe_to_implement=false.
• Tightened stage prompts and compacted prior stage outputs to keep real-runtime reviewer stages structured and bounded.
• Updated docs and regression tests for the candidate-diff requirement.

Verification

• env -u UV_EXCLUDE_NEWER uv run ruff check .
• env -u UV_EXCLUDE_NEWER uv run mypy
• env -u UV_EXCLUDE_NEWER uv run pytest (98 passed, 3 skipped)
• env -u UV_EXCLUDE_NEWER uv lock --check
• Real Antigravity ADC structured-output smoke on google-antigravity 0.1.4:

availability True available {'auth_source': 'application-default-credentials'}
finish_reason done
error None
parsed_output {"ok": true}

Safety

• No auto-merge.
• No unsupported credential scraping.
• Candidate SDK inspection uses temporary isolated virtualenvs.