feat(gateway): add configurable lane queue mode, cap, and overflow

docs/plans/state.json

@@ -13,6 +13,23 @@
       "date": "2026-02-15",
       "summary": "Added docs/architecture/GATEWAY_SESSIONS_AND_QUEUE.md to document how gateway connectionIds map to durable sessionIds, how per-session FIFO lane queueing works, and how agent.cancel behaves."
     },
+    "gateway-lane-queue-policy-phase1": {
+      "status": "completed",
+      "date": "2026-02-16",
+      "updated": "2026-02-16",
+      "summary": "Added configurable gateway lane queue policy (`server.queue`) with mode (`collect|steer|interrupt`), per-lane cap, and overflow behavior (`drop_old|drop_new`). Wired through daemon -> gateway runtime, expanded LaneQueue behavior/tests, and documented the new config in README + default config.",
+      "files_modified": [
+        "src/gateway/lane-queue.ts",
+        "src/gateway/lane-queue.test.ts",
+        "src/gateway/server.ts",
+        "src/daemon/services.ts",
+        "src/config/schema.ts",
+        "src/config/schema.test.ts",
+        "config/default.yaml",
+        "README.md"
+      ],
+      "test_status": "pnpm test:run src/gateway/lane-queue.test.ts src/config/schema.test.ts + pnpm typecheck passing"
+    },
     "docs-gateway-auth-config-keys": {
       "status": "completed",
       "date": "2026-02-15",