feat: add configurable medium model fleet slot

dev/ACTIVE_TASK.json

@@ -1,5 +1,5 @@
 {
-  "task_file": "dev/tasks/DEV-000167-cpu-readiness-client-timeout.json",
-  "task_id": "DEV-000167",
+  "task_file": "dev/tasks/DEV-000168-configurable-medium-fleet-slot.json",
+  "task_id": "DEV-000168",
   "task_revision": 1
 }

dev/tasks/DEV-000168-configurable-medium-fleet-slot.json

@@ -0,0 +1,23 @@
+{
+  "task_id": "DEV-000168",
+  "task_revision": 1,
+  "architecture_revision": "ADR-0018",
+  "base_repo_revision": "205d8f620603ccf3e0138f6beb93156450664314",
+  "risk_tier": "E",
+  "intent": "Make the MEDIUM model-fleet slot a real optional OpenAI-compatible provider path with protected file credentials, discovery, readiness and gateway registration.",
+  "requirement_ids": ["WP-200", "WP-301", "Model fleet/failover"],
+  "allowed_change_scope": {"modules": ["cognitive-worker", "deployment-policy", "tests"], "paths": ["cmd/cognitive-worker/main.go", "cmd/cognitive-worker/main_test.go", "deploy/docker-compose.prod.yml", "tests/cognitive_advisory/cognitive_worker_env_policy.ps1", "tests/cognitive_advisory/cognitive_worker_env_policy_test.ps1", "dev/ACTIVE_TASK.json", "dev/tasks/DEV-000168-configurable-medium-fleet-slot.json"]},
+  "forbidden_change_scope": {"paths": ["architecture/**", "security/**", "database/**", "contracts/**", "adapters/**", ".gitea/**"]},
+  "allowed_architecture_delta": {"new_cross_module_dependencies": 0, "new_canonical_owners": 0, "new_privileges": 1, "new_third_party_dependencies": 0, "new_database_owner_roles": 0},
+  "contracts": {"consume": ["existing provider adapter contract", "existing discovery registration", "existing fleet readiness contract", "existing CredentialRef file contract"], "may_change": []},
+  "semantic_owner": "cognitive-worker/capability registration boundary",
+  "canonical_state": [],
+  "state_transitions": ["MEDIUM endpoint absent -> NOT_CONFIGURED", "MEDIUM endpoint configured -> discovery/readiness registration", "available provider -> eligible gateway binding subject to core registry policy"],
+  "side_effects_and_privileges": ["declares one new deployment configuration surface for an existing read-only secret volume; provider key is resolved only through the existing protected file CredentialRef"],
+  "persistence_and_migrations": ["none"],
+  "failure_retry_restart": ["medium probe has a bounded 10-second client timeout; absent endpoint remains NOT_CONFIGURED; fallback selection remains Lifeboat when preferred tiers are unavailable"],
+  "assumptions": ["A real medium OpenAI-compatible runtime may be supplied later through deployment environment injection", "No production medium runtime is claimed by this change"],
+  "acceptance_scenarios": ["empty medium URL produces NOT_CONFIGURED without startup failure", "configured medium URL is registered for discovery and fleet readiness", "direct medium secret environment is rejected", "medium CredentialRef file is accepted", "CPU/GPU/Lifeboat behavior remains unchanged"],
+  "required_tests": ["go test ./...", "go vet ./...", "preflight", "check-diff", "check-architecture", "independent", "git diff --check", "environment policy tests", "CI", "production fleet readiness"],
+  "terminal_gap_states": ["BLOCKED_BY_MISSING_CAPABILITY", "BLOCKED_BY_CONFLICT"]
+}