docs(plan): add pi canary evaluation gate and tracking (diagram review no topology change)

README.md

@@ -363,6 +363,19 @@ backends:
 
 `pi_embedded` is intended for canary migration cohorts. In spike mode (`no_tools_mode: true`), Flynn keeps tool-oriented turns on native and only routes plain-text turns to Pi.
 
+To evaluate canary performance from audit logs, run:
+
+```bash
+pnpm audit:backend-canary \
+  --audit ~/.local/share/flynn/audit.log \
+  --backend pi_embedded \
+  --baseline native \
+  --session telegram:8367012007 \
+  --format markdown
+```
+
+Phase-2 evaluation checklist and decision template: `docs/plans/pi_embedded_evaluation.md`.
+
 When `args` is non-empty:
 - use `{prompt}` in an argument to inject the full generated prompt directly into argv.
 - if `{prompt}` is not present, Flynn appends backend-specific prompt args.