Standalone timing benchmarks for the renderer's hot paths (initial hydration, callbacks, wildcards, Patch). Kept out of the pytest suite on purpose - timing is noisy, so this reports rather than flaking tests. See .ai/PERFORMANCE.md for the full methodology, profiling guide, and findings.

npm run build                                   # production renderer bundle
python -m benchmarks.run                        # run everything, print a table
python -m benchmarks.run --scenario patch_append_nested   # just one
python -m benchmarks.run --profile wildcard_all_resolve   # CPU-profile one

• scenarios.py - the scenarios (app + interaction + thresholds)
• bench_app.py - serves one scenario in its own process (production bundle)
• run.py - runner, CPU profiler, threshold gating, markdown report
• baseline.json - committed reference the CI job compares against

Add a build/drive pair and register it in scenarios.py:

def _build_x(params): ...        # returns a Dash app; ends its layout with READY
def _drive_x(b, params): ...     # returns {"metric_ms": <in-browser ms>}

scenario(
    name="x", description="...", params={...},
    warn_ms={"metric_ms": 500}, fail_ms={"metric_ms": 2000},
)((_build_x, _drive_x))

b is the browser helper (b.timed, b.render_time, b.reload, b.state, b.graph_time). Every layout must end with the shared READY sentinel so the harness can detect "fully hydrated". Then regenerate baseline.json.