Compare per-test gas between the current branch and a base branch (default: main). Uses `forge test --json` to extract gas per test, then cross-references with test_metadata.json to produce per-test comparison tables grouped by source file. Router gas includes executor delegatecall cost, so it represents the full swap cost. Use when user says "gas compare", "gas report", "gas diff", "compare gas", "gas regression", "gas benchmark", or invokes /gas-compare.
Keep crates/tycho-execution/.gas-compare/test_metadata.json in sync with the high-level TychoRouter test files. Scans crates/tycho-execution/contracts/test/TychoRouter*.t.sol files, diffs against the existing JSON, and adds/removes/updates entries. Use when tests have been added, removed, or renamed. Trigger on: "update test metadata", "sync test metadata", "update gas test list", "new tests added", or invokes /update-gas-test-metadata.