feat: cut over to WASM backend

spikes/wasm-phase5/README.md

@@ -42,11 +42,13 @@ Artifacts are written under `/tmp/uce/wasm-phase5/`:
   - `sqlite-page`: `/demo/sqlite.uce`
   - `component-heavy-starter`: `/examples/uce-starter/?dashboard`
 
-`benchmark.py` also accepts `--wasm-base-url` once a WASM worker endpoint exists.
-When provided, it compares WASM medians against the Phase 5 budget of ≤2× native
-page latency. Workspace birth and internal component call overhead budgets still
-need worker-internal probes; this harness documents the gap rather than faking
-those numbers.
+`benchmark.py` also accepts `--wasm-base-url` when native and WASM are served
+from separate endpoints. For the W5 in-place cutover, use
+`--backend-label wasm --compare-native-json <native benchmark.json>` after
+switching `/etc/uce/settings.cfg` to the WASM backend; this compares WASM
+medians against the Phase 5 budget of ≤2× native page latency. W5 worker builds
+emit `X-UCE-Wasm-Workspace-Birth-Us` and component resolve probe headers on
+WASM-served responses.
 
 A durable informational baseline snapshot is kept in `reports/`. Paired
 native/WASM runs still recompute native medians for the actual budget decision.