feat: add @uncaged/uwf-agent-kit — agent CLI framework

- createAgent() API for building agent CLIs
- Context builder: reads CAS chain, builds AgentContext
- Extract: LLM-based structured output extraction
- StepNode writer: writes to CAS without touching threads.yaml
- Stdout: outputs StepNode hash

Refs #309, #314

packages/uwf-agent-kit/__tests__/resolve-extract-model.test.ts

@@ -0,0 +1,42 @@
+import { describe, expect, test } from "bun:test";
+import type { WorkflowConfig } from "@uncaged/uwf-protocol";
+import { resolveExtractModelAlias } from "../src/extract.js";
+
+function baseConfig(overrides: Partial<WorkflowConfig> = {}): WorkflowConfig {
+  return {
+    providers: {},
+    models: {
+      sonnet: { provider: "openrouter", name: "anthropic/claude-sonnet-4" },
+      "gpt4o-mini": { provider: "openai", name: "gpt-4o-mini" },
+    },
+    agents: {},
+    defaultAgent: "hermes",
+    agentOverrides: null,
+    defaultModel: "sonnet",
+    modelOverrides: null,
+    ...overrides,
+  };
+}
+
+describe("resolveExtractModelAlias", () => {
+  test("uses modelOverrides.extract when set", () => {
+    const config = baseConfig({
+      modelOverrides: { extract: "gpt4o-mini" },
+    });
+    expect(resolveExtractModelAlias(config)).toBe("gpt4o-mini");
+  });
+
+  test("falls back to models.extract alias when present", () => {
+    const config = baseConfig({
+      models: {
+        extract: { provider: "openai", name: "gpt-4o-mini" },
+        sonnet: { provider: "openrouter", name: "anthropic/claude-sonnet-4" },
+      },
+    });
+    expect(resolveExtractModelAlias(config)).toBe("extract");
+  });
+
+  test("falls back to defaultModel", () => {
+    expect(resolveExtractModelAlias(baseConfig())).toBe("sonnet");
+  });
+});