feat(cag): memory standing-context adapter, warmup semaphore, cache-aware routing

Issue #44: code-register memory adapter with standing-context resource; fix
dispatcher method-level Auth.Capability override (was always using verb-derived
capability, ignoring per-method Auth field).

Issue #45: per-backend bounded in-memory queue (VLLM_MAX_QUEUE_DEPTH=20) +
concurrency semaphore (VLLM_MAX_NUM_SEQS=4); warmup requests (X-Poimen-Warmup:
true) sleep WARMUP_DELAY_MS before queue entry; /metrics endpoint wired.

Issue #46: rendezvous-hash backend selection on X-Poimen-Cache-Key; round-robin
fallback; MarkFailed excludes unhealthy backends 30s; ModifyResponse captures
vllm-num-cached-tokens + emits structured log + increments counter.

Closes #44 Closes #45 Closes #46

cmd/gateway/main.go

@@ -12,6 +12,7 @@ import (
 	"forgejo.riotpiao.com/rock/homelab-frontend/internal/auth"
 	"forgejo.riotpiao.com/rock/homelab-frontend/internal/config"
 	"forgejo.riotpiao.com/rock/homelab-frontend/internal/notification"
+	"forgejo.riotpiao.com/rock/homelab-frontend/internal/observability"
 	"forgejo.riotpiao.com/rock/homelab-frontend/internal/proxy"
 	"forgejo.riotpiao.com/rock/homelab-frontend/internal/server"
 	"forgejo.riotpiao.com/rock/homelab-frontend/internal/serviceadapter"
@@ -112,6 +113,10 @@ func main() {
 	poimenAdapter := serviceadapter.NewPoimenAdapter(temporalHandler)
 	_ = registry.Add(poimenAdapter)
 
+	// Add memory service adapter (code-registered; config memory entry is skipped).
+	// Includes standing-context resource for CAG support (issue #44).
+	_ = registry.Add(serviceadapter.NewMemoryAdapter())
+
 	// Add other adapters from config (skip if already registered in code)
 	for _, a := range cfg.Adapters {
 		if existing := registry.Get(a.ServiceName); existing != nil {
@@ -135,6 +140,7 @@ func main() {
 	// Create router that handles health endpoints, X-Service (ServiceAdapter) routing,
 	// temporal endpoints, and passes others to upstream handler
 	router := server.NewRouter(healthChecker, dispatcher, temporalHandler, upstreamHandler)
+	router.SetMetricsHandler(observability.NewMetricsHandler(observability.Global()))
 
 	// Wrap router with tracing middleware
 	tracedRouter := tracing.Middleware(router)