feat(router): entity caching with L1/L2, shadow mode, and per-request cache controls

Extracted from jensneuse/entity-caching-v2 (PR #2777) — router layer, stacked on
the demo PR. Entity cache OTEL/Prometheus metrics are split into the next PR in
the stack; this PR contains the cache engine and wiring only.

- router/pkg/entitycache: in-memory L1, Redis L2, circuit breaker
- router/core: factoryresolver mapping of proto cache config to planner metadata,
  graph server wiring, per-request cache-control headers, plan generator nil guard
- config schema + defaults for entity_caching (metrics opt-in keys land with the
  metrics PR)
- graphql-go-tools bumped to PR #1259 HEAD (resolver/planner side)
- router-tests/entity_caching: integration suite consuming the demo module's
  cachetest subgraphs; compose tool for testdata/config.json

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: 2 people

router-tests/entity_caching/Makefile

@@ -0,0 +1,6 @@
+.PHONY: compose
+
+compose:
+	go run ./cmd/compose
+	jq . testdata/config.json > testdata/config.json.tmp
+	mv testdata/config.json.tmp testdata/config.json

router-tests/entity_caching/cmd/compose/main.go

@@ -0,0 +1,88 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	composition "github.com/wundergraph/cosmo/composition-go"
+)
+
+func main() {
+	itemsSchema, err := os.ReadFile("../../demo/pkg/subgraphs/cachetest/items/subgraph/schema.graphqls")
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "error reading items schema: %v\n", err)
+		os.Exit(1)
+	}
+	detailsSchema, err := os.ReadFile("../../demo/pkg/subgraphs/cachetest/details/subgraph/schema.graphqls")
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "error reading details schema: %v\n", err)
+		os.Exit(1)
+	}
+	inventorySchema, err := os.ReadFile("../../demo/pkg/subgraphs/cachetest/inventory/subgraph/schema.graphqls")
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "error reading inventory schema: %v\n", err)
+		os.Exit(1)
+	}
+	viewerSchema, err := os.ReadFile("../../demo/pkg/subgraphs/cachetest/viewer/subgraph/schema.graphqls")
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "error reading viewer schema: %v\n", err)
+		os.Exit(1)
+	}
+	articlesSchema, err := os.ReadFile("../../demo/pkg/subgraphs/cachetest/articles/subgraph/schema.graphqls")
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "error reading articles schema: %v\n", err)
+		os.Exit(1)
+	}
+	articlesMetaSchema, err := os.ReadFile("../../demo/pkg/subgraphs/cachetest/articlesmeta/subgraph/schema.graphqls")
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "error reading articlesmeta schema: %v\n", err)
+		os.Exit(1)
+	}
+
+	result, err := composition.BuildRouterConfiguration(
+		&composition.Subgraph{
+			Name:   "items",
+			Schema: string(itemsSchema),
+			URL:    "http://items.entity-cache-test.local/graphql",
+		},
+		&composition.Subgraph{
+			Name:   "details",
+			Schema: string(detailsSchema),
+			URL:    "http://details.entity-cache-test.local/graphql",
+		},
+		&composition.Subgraph{
+			Name:   "inventory",
+			Schema: string(inventorySchema),
+			URL:    "http://inventory.entity-cache-test.local/graphql",
+		},
+		&composition.Subgraph{
+			Name:   "viewer",
+			Schema: string(viewerSchema),
+			URL:    "http://viewer.entity-cache-test.local/graphql",
+		},
+		&composition.Subgraph{
+			Name:   "articles",
+			Schema: string(articlesSchema),
+			URL:    "http://articles.entity-cache-test.local/graphql",
+		},
+		&composition.Subgraph{
+			Name:   "articlesmeta",
+			Schema: string(articlesMetaSchema),
+			URL:    "http://articlesmeta.entity-cache-test.local/graphql",
+		},
+	)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "composition error: %v\n", err)
+		os.Exit(1)
+	}
+
+	if err := os.MkdirAll("testdata", 0o755); err != nil {
+		fmt.Fprintf(os.Stderr, "error creating testdata dir: %v\n", err)
+		os.Exit(1)
+	}
+	if err := os.WriteFile("testdata/config.json", []byte(result), 0o644); err != nil {
+		fmt.Fprintf(os.Stderr, "error writing config: %v\n", err)
+		os.Exit(1)
+	}
+	fmt.Printf("config written to testdata/config.json (%d bytes)\n", len(result))
+}