v2.3 task 04: replacement ctxguard_router_test.go for the new refusal body; run notes

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/plans/v2.3/04-ctx-error-docs.md

@@ -18,8 +18,9 @@ shape, so the client handles crossbar's refusal like the server's:
 
 ## Files
 
-- Copy: the **replacement** `internal/proxy/ctxguard_test.go` (was v2's; only the 400-body
-  assertions changed; the v2.3 copy is now protected)
+- Copy: the **replacements** `internal/proxy/ctxguard_test.go` (was v2's) and
+  `internal/proxy/ctxguard_router_test.go` (was v2.1's); only their 400-body assertions changed;
+  the v2.3 copies are now protected
 - Modify: `internal/proxy/ctxguard.go` (`refuseCtx`), `README.md`, `docs/implementer-log.md`
 
 ## Rules