feat(uwf-agent-kit): frontmatter fast path + prompt injection

Port RFC #351 frontmatter markdown to uwf-* path:
- tryFrontmatterFastPath(): parse → validate → JSON Schema check via json-cas
- Happy path skips LLM extract, fallback to existing extract()
- buildOutputFormatInstruction(): generates deliverable format from JSON Schema
- Injected into agent context before execution
- Scope reminder: 'Focus exclusively on YOUR role's deliverable'
- 14 new tests (vitest)

Closes #355

.gitignore

@@ -10,3 +10,4 @@ xiaoju/
 solve-issue-entry.ts
 packages/workflow-template-develop/develop.esm.js
 .DS_Store
+*.py

packages/cli-uwf/src/cli.ts

@@ -1,11 +1,14 @@
 #!/usr/bin/env bun
 
 import { Command } from "commander";
+import type { ThreadId } from "@uncaged/uwf-protocol";
 
 import {
   cmdThreadFork,
   cmdThreadKill,
   cmdThreadList,
+  cmdThreadRead,
+  THREAD_READ_DEFAULT_QUOTA,
   cmdThreadShow,
   cmdThreadStart,
   cmdThreadStep,
@@ -158,6 +161,28 @@ thread
     });
   });
 
+thread
+  .command("read")
+  .description("Read thread context as human-readable markdown")
+  .argument("<thread-id>", "Thread ULID")
+  .option("--quota <chars>", "Max output characters", String(THREAD_READ_DEFAULT_QUOTA))
+  .option("--before <step-hash>", "Load steps before this hash (exclusive)")
+  .option("--start", "Include start step in output")
+  .option("--detail", "Expand detail content for each step")
+  .action((threadId: string, opts: { quota: string; before: string | undefined; start: boolean; detail: boolean }) => {
+    const storageRoot = resolveStorageRoot();
+    runAction(async () => {
+      const quota = Number.parseInt(opts.quota, 10);
+      if (!Number.isFinite(quota) || quota < 1) {
+        process.stderr.write("invalid --quota: must be a positive integer\n");
+        process.exit(1);
+      }
+      const before = opts.before ?? null;
+      const markdown = await cmdThreadRead(storageRoot, threadId as ThreadId, quota, before, opts.start ?? false, opts.detail ?? false);
+      process.stdout.write(markdown.endsWith("\n") ? markdown : `${markdown}\n`);
+    });
+  });
+
 thread
   .command("fork")
   .description("Fork a thread from a specific step")

packages/cli-uwf/src/commands/thread.ts

@@ -1,6 +1,8 @@
 import { execFileSync } from "node:child_process";
 
-import { validate } from "@uncaged/json-cas";
+import { getSchema, validate } from "@uncaged/json-cas";
+import type { JSONSchema, Store as CasStore } from "@uncaged/json-cas";
+import { stringify } from "yaml";
 import { getEnvPath, loadWorkflowConfig } from "@uncaged/uwf-agent-kit";
 import { evaluate } from "@uncaged/uwf-moderator";
 import type {
@@ -40,6 +42,7 @@ import {
 import { isCasRef } from "../validate.js";
 
 const END_ROLE = "$END";
+export const THREAD_READ_DEFAULT_QUOTA = 4000;
 
 type ChainState = {
   startHash: CasRef;
@@ -48,6 +51,12 @@ type ChainState = {
   headIsStart: boolean;
 };
 
+type OrderedStepItem = {
+  hash: CasRef;
+  payload: StepNodePayload;
+  timestamp: number;
+};
+
 export type KillOutput = {
   thread: ThreadId;
   archived: boolean;
@@ -266,6 +275,215 @@ function expandOutput(uwf: UwfStore, outputRef: CasRef): unknown {
   return node.payload;
 }
 
+/**
+ * Recursively expand all cas_ref fields in a CAS node's payload,
+ * replacing hash strings with the referenced node's expanded payload.
+ */
+function expandDeep(store: CasStore, hash: CasRef, visited?: Set<string>): unknown {
+  const seen = visited ?? new Set<string>();
+  if (seen.has(hash)) return hash; // cycle guard
+  seen.add(hash);
+
+  const node = store.get(hash);
+  if (node === null) return hash;
+
+  const schema = getSchema(store, node.type);
+  if (schema === null) return node.payload;
+
+  return expandValue(store, schema, node.payload, seen);
+}
+
+function expandValue(store: CasStore, schema: JSONSchema, value: unknown, visited: Set<string>): unknown {
+  // If this field is a cas_ref, expand it
+  if (schema.format === "cas_ref") {
+    if (typeof value === "string") {
+      return expandDeep(store, value as CasRef, visited);
+    }
+    return value;
+  }
+
+  // anyOf (nullable refs)
+  if (Array.isArray(schema.anyOf)) {
+    for (const sub of schema.anyOf as JSONSchema[]) {
+      if (sub.format === "cas_ref" && typeof value === "string") {
+        return expandDeep(store, value as CasRef, visited);
+      }
+    }
+    return value;
+  }
+
+  // Array of cas_ref items
+  if (schema.type === "array" && schema.items && Array.isArray(value)) {
+    const itemSchema = schema.items as JSONSchema;
+    return (value as unknown[]).map((item) => expandValue(store, itemSchema, item, visited));
+  }
+
+  // Object with properties
+  if (value !== null && typeof value === "object" && !Array.isArray(value) && schema.properties) {
+    const props = schema.properties as Record<string, JSONSchema>;
+    const obj = value as Record<string, unknown>;
+    const result: Record<string, unknown> = {};
+    for (const [key, val] of Object.entries(obj)) {
+      const propSchema = props[key];
+      result[key] = propSchema ? expandValue(store, propSchema, val, visited) : val;
+    }
+    return result;
+  }
+
+  return value;
+}
+
+function collectOrderedSteps(
+  uwf: UwfStore,
+  headHash: CasRef,
+  chain: ChainState,
+): OrderedStepItem[] {
+  let hash: CasRef | null = headHash;
+  const hashToNode = new Map<string, { payload: StepNodePayload; timestamp: number }>();
+  while (hash !== null) {
+    const node = uwf.store.get(hash);
+    if (node === null || node.type !== uwf.schemas.stepNode) {
+      break;
+    }
+    const payload = node.payload as StepNodePayload;
+    hashToNode.set(hash, { payload, timestamp: node.timestamp });
+    hash = payload.prev;
+  }
+
+  let cur: CasRef | null = chain.headIsStart ? null : headHash;
+  const ordered: OrderedStepItem[] = [];
+  while (cur !== null) {
+    const entry = hashToNode.get(cur);
+    if (entry === undefined) {
+      break;
+    }
+    ordered.push({ hash: cur, ...entry });
+    cur = entry.payload.prev;
+  }
+  ordered.reverse();
+  return ordered;
+}
+
+function formatYaml(value: unknown): string {
+  return stringify(value).trimEnd();
+}
+
+function formatCompactStep(index: number, item: OrderedStepItem, outputYaml: string): string {
+  return [
+    `## Step ${index}: ${item.payload.role}`,
+    "",
+    `- **Hash:** \`${item.hash}\``,
+    `- **Agent:** ${item.payload.agent}`,
+    "",
+    "### Output",
+    "",
+    "```yaml",
+    outputYaml,
+    "```",
+  ].join("\n");
+}
+
+function formatThreadReadMarkdown(options: {
+  threadId: ThreadId;
+  workflowName: string;
+  workflowHash: CasRef;
+  prompt: string;
+  ordered: OrderedStepItem[];
+  uwf: UwfStore;
+  workflow: WorkflowPayload;
+  quota: number;
+  before: CasRef | null;
+  showStart: boolean;
+  showDetail: boolean;
+}): string {
+  const { ordered, uwf, workflow, quota, before, showStart, showDetail } = options;
+
+  // Determine which steps to consider
+  let candidates = ordered;
+  if (before !== null) {
+    const idx = candidates.findIndex((s) => s.hash === before);
+    if (idx === -1) {
+      fail(`step ${before} not found in thread ${options.threadId}`);
+    }
+    candidates = candidates.slice(0, idx);
+  }
+
+  // Walk backward from newest, accumulating chars until quota exceeded
+  const selected: OrderedStepItem[] = [];
+  let totalChars = 0;
+  for (let i = candidates.length - 1; i >= 0; i--) {
+    const item = candidates[i];
+    if (item === undefined) continue;
+    const outputYaml = formatYaml(expandOutput(uwf, item.payload.output));
+    const blockLen = formatCompactStep(i + 1, item, outputYaml).length;
+    selected.unshift(item);
+    totalChars += blockLen;
+    if (totalChars > quota) break;
+  }
+
+  const skippedCount = candidates.length - selected.length;
+  const parts: string[] = [];
+
+  // Start section
+  if (before === null || showStart) {
+    parts.push(
+      [
+        `# Thread \`${options.threadId}\``,
+        "",
+        `**Workflow:** ${options.workflowName} (\`${options.workflowHash}\`)`,
+        "",
+        "## Task",
+        "",
+        options.prompt,
+      ].join("\n"),
+    );
+  }
+
+  // Skip hint
+  if (skippedCount > 0 && selected.length > 0) {
+    const firstSelected = selected[0];
+    if (firstSelected !== undefined) {
+      parts.push(
+        `*(${skippedCount} earlier step${skippedCount > 1 ? "s" : ""}, load with \`uwf thread read ${options.threadId} --before ${firstSelected.hash}\`)*`,
+      );
+    }
+  }
+
+  // Step blocks
+  const startIndex = candidates.length - selected.length;
+  for (let i = 0; i < selected.length; i++) {
+    const item = selected[i];
+    if (item === undefined) continue;
+    const stepNum = startIndex + i + 1;
+    const outputYaml = formatYaml(expandOutput(uwf, item.payload.output));
+    const ts = new Date(item.timestamp).toISOString().replace("T", " ").replace(/\.\d+Z$/, "");
+    const stepLines = [
+      `## Step ${stepNum}: ${item.payload.role} \`${item.hash}\``,
+      `**Agent:** ${item.payload.agent} | **Time:** ${ts}`,
+    ];
+    const roleDef = workflow.roles[item.payload.role];
+    if (roleDef) {
+      stepLines.push("", "### Prompt", "", roleDef.systemPrompt);
+    }
+    stepLines.push(
+      "",
+      "### Output",
+      "",
+      "```yaml",
+      outputYaml,
+      "```",
+    );
+    if (showDetail && item.payload.detail) {
+      const detailExpanded = expandDeep(uwf.store, item.payload.detail);
+      const detailYaml = formatYaml(detailExpanded);
+      stepLines.push("", "### Detail", "", "```yaml", detailYaml, "```");
+    }
+    parts.push(stepLines.join("\n"));
+  }
+
+  return parts.join("\n\n---\n\n");
+}
+
 function buildModeratorContext(uwf: UwfStore, chain: ChainState): ModeratorContext {
   const chronological = [...chain.stepsNewestFirst].reverse();
   const steps: StepContext[] = chronological.map((step) => ({
@@ -475,31 +693,7 @@ export async function cmdThreadSteps(
   };
 
   const stepEntries: StepEntry[] = [];
-
-  // Walk again to get hashes for each step
-  let hash: CasRef | null = headHash;
-  const hashToNode = new Map<string, { payload: StepNodePayload; timestamp: number }>();
-  while (hash !== null) {
-    const node = uwf.store.get(hash);
-    if (node === null || node.type !== uwf.schemas.stepNode) {
-      break;
-    }
-    const payload = node.payload as StepNodePayload;
-    hashToNode.set(hash, { payload, timestamp: node.timestamp });
-    hash = payload.prev;
-  }
-
-  // Build chronological list with hashes
-  // Walk from start's next to head
-  let cur: CasRef | null = chain.headIsStart ? null : headHash;
-  const ordered: { hash: CasRef; payload: StepNodePayload; timestamp: number }[] = [];
-  while (cur !== null) {
-    const entry = hashToNode.get(cur);
-    if (entry === undefined) break;
-    ordered.push({ hash: cur, ...entry });
-    cur = entry.payload.prev;
-  }
-  ordered.reverse();
+  const ordered = collectOrderedSteps(uwf, headHash, chain);
 
   for (const item of ordered) {
     stepEntries.push({
@@ -519,6 +713,35 @@ export async function cmdThreadSteps(
   };
 }
 
+export async function cmdThreadRead(
+  storageRoot: string,
+  threadId: ThreadId,
+  quota: number = THREAD_READ_DEFAULT_QUOTA,
+  before: CasRef | null = null,
+  showStart: boolean = false,
+  showDetail: boolean = false,
+): Promise<string> {
+  const headHash = await resolveHeadHash(storageRoot, threadId);
+  const uwf = await createUwfStore(storageRoot);
+  const chain = walkChain(uwf, headHash);
+  const workflow = loadWorkflowPayload(uwf, chain.start.workflow);
+  const ordered = collectOrderedSteps(uwf, headHash, chain);
+
+  return formatThreadReadMarkdown({
+    threadId,
+    workflowName: workflow.name,
+    workflowHash: chain.start.workflow,
+    prompt: chain.start.prompt,
+    ordered,
+    uwf,
+    workflow,
+    quota,
+    before,
+    showStart,
+    showDetail,
+  });
+}
+
 export async function cmdThreadFork(
   storageRoot: string,
   stepHash: CasRef,

packages/uwf-agent-hermes/__tests__/session-detail.test.ts

@@ -16,7 +16,12 @@ describe("parseSessionIdFromStdout", () => {
     expect(parseSessionIdFromStdout(stdout)).toBe("20260518_223724_45ab80");
   });
 
-  test("returns null when trailing line is not session_id", () => {
+  test("reads session_id from the first line (quiet mode)", () => {
+    const stdout = "session_id: 20260518_165315_3467a1\nHello world\n";
+    expect(parseSessionIdFromStdout(stdout)).toBe("20260518_165315_3467a1");
+  });
+
+  test("returns null when no session_id line present", () => {
     expect(parseSessionIdFromStdout("only assistant text\n")).toBeNull();
   });
 });

packages/uwf-agent-hermes/src/hermes.ts

@@ -43,7 +43,7 @@ export function buildHermesPrompt(ctx: AgentContext): string {
   return parts.join("\n");
 }
 
-function spawnHermesChat(prompt: string): Promise<string> {
+function spawnHermesChat(prompt: string): Promise<{ stdout: string; stderr: string }> {
   return new Promise((resolve, reject) => {
     const args = [
       "chat",
@@ -76,7 +76,7 @@ function spawnHermesChat(prompt: string): Promise<string> {
 
     child.on("close", (code) => {
       if (code === 0) {
-        resolve(stdout);
+        resolve({ stdout, stderr });
         return;
       }
       const detail = stderr.trim() !== "" ? ` stderr=${stderr.trim()}` : "";
@@ -87,10 +87,11 @@ function spawnHermesChat(prompt: string): Promise<string> {
 
 async function runHermes(ctx: AgentContext): Promise<AgentRunResult> {
   const fullPrompt = buildHermesPrompt(ctx);
-  const rawOutput = await spawnHermesChat(fullPrompt);
+  const { stdout, stderr } = await spawnHermesChat(fullPrompt);
   const { store } = ctx;
 
-  const sessionId = parseSessionIdFromStdout(rawOutput);
+  // --quiet mode: session_id may be on stdout or stderr
+  const sessionId = parseSessionIdFromStdout(stderr) ?? parseSessionIdFromStdout(stdout);
   if (sessionId !== null) {
     const session = await loadHermesSession(sessionId);
     if (session !== null) {
@@ -99,8 +100,8 @@ async function runHermes(ctx: AgentContext): Promise<AgentRunResult> {
     }
   }
 
-  const detailHash = await storeHermesRawOutput(store, rawOutput);
-  return { output: rawOutput, detailHash };
+  const detailHash = await storeHermesRawOutput(store, stdout);
+  return { output: stdout, detailHash };
 }
 
 /** Agent CLI factory: parses argv, runs Hermes, extracts output, writes StepNode. */

packages/uwf-agent-hermes/src/session-detail.ts

@@ -24,19 +24,14 @@ export function getHermesSessionPath(sessionId: string): string {
   return join(getHermesSessionsDir(), `session_${sessionId}.json`);
 }
 
-/** Parse `session_id: …` from the last non-empty line of Hermes stdout. */
+/** Parse `session_id: …` from any line of Hermes stdout. */
 export function parseSessionIdFromStdout(stdout: string): string | null {
-  const lines = stdout.split(/\r?\n/).map((line) => line.trim());
-  for (let i = lines.length - 1; i >= 0; i--) {
-    const line = lines[i];
-    if (line === undefined || line === "") {
-      continue;
-    }
-    const match = SESSION_ID_LINE.exec(line);
+  const lines = stdout.split(/\r?\n/);
+  for (const line of lines) {
+    const match = SESSION_ID_LINE.exec(line.trim());
     if (match?.[1] !== undefined) {
       return match[1];
     }
-    break;
   }
   return null;
 }

packages/uwf-agent-kit/__tests__/build-output-format-instruction.test.ts

@@ -0,0 +1,89 @@
+import { describe, expect, test } from "vitest";
+
+import { buildOutputFormatInstruction } from "../src/build-output-format-instruction.js";
+
+describe("buildOutputFormatInstruction", () => {
+  test("always includes the frontmatter example block", () => {
+    const result = buildOutputFormatInstruction({});
+    expect(result).toContain("---");
+    expect(result).toContain("status: done");
+    expect(result).toContain("confidence:");
+    expect(result).toContain("scope: role");
+  });
+
+  test("always marks frontmatter as the primary deliverable", () => {
+    const result = buildOutputFormatInstruction({});
+    expect(result).toContain("primary deliverable");
+  });
+
+  test("lists fields from a flat object schema", () => {
+    const schema = {
+      type: "object",
+      properties: {
+        status: { type: "string" },
+        confidence: { type: "number" },
+      },
+    };
+    const result = buildOutputFormatInstruction(schema);
+    expect(result).toContain("`status`");
+    expect(result).toContain("`confidence`");
+  });
+
+  test("lists union of fields from an anyOf schema", () => {
+    const schema = {
+      anyOf: [
+        {
+          type: "object",
+          properties: { alpha: { type: "string" } },
+        },
+        {
+          type: "object",
+          properties: { beta: { type: "number" } },
+        },
+      ],
+    };
+    const result = buildOutputFormatInstruction(schema);
+    expect(result).toContain("`alpha`");
+    expect(result).toContain("`beta`");
+  });
+
+  test("lists union of fields from a oneOf schema", () => {
+    const schema = {
+      oneOf: [
+        {
+          type: "object",
+          properties: { foo: { type: "string" } },
+        },
+        {
+          type: "object",
+          properties: { bar: { type: "boolean" } },
+        },
+      ],
+    };
+    const result = buildOutputFormatInstruction(schema);
+    expect(result).toContain("`foo`");
+    expect(result).toContain("`bar`");
+  });
+
+  test("falls back gracefully for a non-object schema with no properties", () => {
+    const result = buildOutputFormatInstruction({ type: "string" });
+    expect(result).toContain("schema fields will be extracted automatically");
+  });
+
+  test("does not list a field more than once for a union with overlapping keys", () => {
+    const schema = {
+      anyOf: [
+        { type: "object", properties: { shared: { type: "string" } } },
+        { type: "object", properties: { shared: { type: "number" } } },
+      ],
+    };
+    const result = buildOutputFormatInstruction(schema);
+    const matches = [...result.matchAll(/`shared`/g)];
+    expect(matches.length).toBe(1);
+  });
+
+  test("includes focus reminder about role scope", () => {
+    const result = buildOutputFormatInstruction({});
+    expect(result).toContain("Focus exclusively on YOUR role");
+  });
+});

packages/uwf-agent-kit/__tests__/frontmatter-fast-path.test.ts

@@ -0,0 +1,136 @@
+import { describe, expect, test } from "vitest";
+
+import { createMemoryStore, putSchema } from "@uncaged/json-cas";
+
+import { tryFrontmatterFastPath } from "../src/frontmatter.js";
+
+// ── Helpers ───────────────────────────────────────────────────────────────────
+
+/** JSON Schema that exactly matches the AgentFrontmatter fields. */
+const FRONTMATTER_SCHEMA = {
+  type: "object",
+  properties: {
+    status: { anyOf: [{ type: "string" }, { type: "null" }] },
+    next: { anyOf: [{ type: "string" }, { type: "null" }] },
+    confidence: { anyOf: [{ type: "number" }, { type: "null" }] },
+    artifacts: { type: "array", items: { type: "string" } },
+    scope: { type: "string" },
+  },
+  required: ["status", "next", "confidence", "artifacts", "scope"],
+  additionalProperties: false,
+};
+
+/** JSON Schema that requires a non-frontmatter field — fast path must not satisfy it. */
+const STRICT_SCHEMA = {
+  type: "object",
+  properties: {
+    requiredField: { type: "string" },
+  },
+  required: ["requiredField"],
+  additionalProperties: false,
+};
+
+async function makeStoreWithSchema(schema: Record<string, unknown>) {
+  const store = createMemoryStore();
+  const schemaHash = await putSchema(store, schema);
+  return { store, schemaHash };
+}
+
+// ── Happy path ─────────────────────────────────────────────────────────────────
+
+describe("tryFrontmatterFastPath — happy path", () => {
+  test("parses valid frontmatter and returns outputHash + stripped body", async () => {
+    const { store, schemaHash } = await makeStoreWithSchema(FRONTMATTER_SCHEMA);
+
+    const raw = [
+      "---",
+      "status: done",
+      "next: reviewer",
+      "confidence: 0.9",
+      "artifacts: [src/foo.ts]",
+      "scope: role",
+      "---",
+      "",
+      "## Summary",
+      "Work is complete.",
+    ].join("\n");
+
+    const result = await tryFrontmatterFastPath(raw, schemaHash, store);
+
+    expect(result).not.toBeNull();
+    expect(result?.body).toContain("## Summary");
+    expect(result?.body).toContain("Work is complete.");
+    expect(result?.body).not.toContain("status: done");
+    expect(typeof result?.outputHash).toBe("string");
+    expect((result?.outputHash ?? "").length).toBeGreaterThan(0);
+  });
+
+  test("stored CAS node payload matches frontmatter fields", async () => {
+    const { store, schemaHash } = await makeStoreWithSchema(FRONTMATTER_SCHEMA);
+
+    const raw = "---\nstatus: done\nnext: null\nconfidence: null\nartifacts: []\nscope: role\n---\n\nBody.";
+
+    const result = await tryFrontmatterFastPath(raw, schemaHash, store);
+    expect(result).not.toBeNull();
+
+    const node = store.get(result!.outputHash);
+    expect(node).not.toBeNull();
+    const payload = node!.payload as Record<string, unknown>;
+    expect(payload.status).toBe("done");
+    expect(payload.next).toBeNull();
+    expect(payload.confidence).toBeNull();
+    expect(payload.artifacts).toEqual([]);
+    expect(payload.scope).toBe("role");
+  });
+});
+
+// ── Fallback: no frontmatter ───────────────────────────────────────────────────
+
+describe("tryFrontmatterFastPath — fallback: no frontmatter", () => {
+  test("returns null for plain markdown without frontmatter block", async () => {
+    const { store, schemaHash } = await makeStoreWithSchema(FRONTMATTER_SCHEMA);
+
+    const result = await tryFrontmatterFastPath(
+      "This is plain markdown without any frontmatter.",
+      schemaHash,
+      store,
+    );
+
+    expect(result).toBeNull();
+  });
+});
+
+// ── Fallback: invalid frontmatter ─────────────────────────────────────────────
+
+describe("tryFrontmatterFastPath — fallback: invalid frontmatter", () => {
+  test("returns null when confidence is out of range [0, 1]", async () => {
+    const { store, schemaHash } = await makeStoreWithSchema(FRONTMATTER_SCHEMA);
+
+    const raw = "---\nstatus: done\nconfidence: 1.5\nscope: role\n---\n\nBody.";
+
+    const result = await tryFrontmatterFastPath(raw, schemaHash, store);
+    expect(result).toBeNull();
+  });
+
+  test("returns null when next contains whitespace", async () => {
+    const { store, schemaHash } = await makeStoreWithSchema(FRONTMATTER_SCHEMA);
+
+    const raw = "---\nstatus: done\nnext: some role\nscope: role\n---\n\nBody.";
+
+    const result = await tryFrontmatterFastPath(raw, schemaHash, store);
+    expect(result).toBeNull();
+  });
+});
+
+// ── Fallback: schema mismatch ─────────────────────────────────────────────────
+
+describe("tryFrontmatterFastPath — fallback: schema mismatch", () => {
+  test("returns null when outputSchema requires fields not in frontmatter", async () => {
+    const { store, schemaHash } = await makeStoreWithSchema(STRICT_SCHEMA);
+
+    const raw = "---\nstatus: done\nscope: role\n---\n\nBody.";
+
+    const result = await tryFrontmatterFastPath(raw, schemaHash, store);
+    expect(result).toBeNull();
+  });
+});

packages/uwf-agent-kit/package.json

@@ -21,6 +21,7 @@
     "@uncaged/json-cas": "^0.3.0",
     "@uncaged/json-cas-fs": "^0.3.0",
     "@uncaged/uwf-protocol": "workspace:^",
+    "@uncaged/workflow-util": "workspace:^",
     "dotenv": "^16.6.1",
     "yaml": "^2.8.4"
   },

packages/uwf-agent-kit/src/build-output-format-instruction.ts

@@ -0,0 +1,75 @@
+import type { JSONSchema } from "@uncaged/json-cas";
+
+/**
+ * Extract top-level property names from a JSON Schema object.
+ *
+ * Handles:
+ * - Object schemas with a `properties` key
+ * - Union schemas via `anyOf` / `oneOf` — union of all variant property names
+ *
+ * Returns an empty array for schemas with no inspectable property definitions.
+ */
+function extractSchemaFields(schema: JSONSchema): string[] {
+  if (typeof schema.properties === "object" && schema.properties !== null) {
+    return Object.keys(schema.properties as Record<string, unknown>);
+  }
+
+  const unionKey = Array.isArray(schema.anyOf)
+    ? "anyOf"
+    : Array.isArray(schema.oneOf)
+      ? "oneOf"
+      : null;
+
+  if (unionKey !== null) {
+    const variants = schema[unionKey] as JSONSchema[];
+    const fieldSet = new Set<string>();
+    for (const variant of variants) {
+      for (const field of extractSchemaFields(variant)) {
+        fieldSet.add(field);
+      }
+    }
+    return [...fieldSet];
+  }
+
+  return [];
+}
+
+/**
+ * Build a concise output format instruction block for an agent role.
+ *
+ * The instruction describes the expected frontmatter markdown format and lists
+ * the meta fields derived from the JSON Schema.  It is prepended to the agent's
+ * system prompt so the deliverable format is the first thing the agent sees.
+ */
+export function buildOutputFormatInstruction(schema: JSONSchema): string {
+  const fields = extractSchemaFields(schema);
+
+  const fieldList =
+    fields.length > 0
+      ? fields.map((f) => `  - \`${f}\``).join("\n")
+      : "  (schema fields will be extracted automatically)";
+
+  return `## Deliverable Format
+
+Your response MUST begin with a YAML frontmatter block followed by your markdown work:
+
+\`\`\`
+---
+status: done          # done | needs_input | in_progress | failed
+next: <role-name>     # suggested next role, or omit
+confidence: 0.9       # 0.0–1.0, your self-assessed confidence
+artifacts:            # list of file paths or CAS hashes you produced
+  - path/to/file.ts
+scope: role           # role | thread
+---
+
+... your markdown work here ...
+\`\`\`
+
+The frontmatter is the **primary deliverable** — the engine reads it directly.
+Your meta output must satisfy these fields:
+
+${fieldList}
+
+Focus exclusively on YOUR role's deliverable. Do not perform actions outside your role's scope.`;
+}

packages/uwf-agent-kit/src/context.ts

@@ -152,6 +152,7 @@ export async function buildContext(threadId: ThreadId, role: string): Promise<Ag
     steps,
     workflow,
     store,
+    outputFormatInstruction: "",
   };
 }
 
@@ -196,6 +197,7 @@ export async function buildContextWithMeta(
     steps,
     workflow,
     store,
+    outputFormatInstruction: "",
     meta: { storageRoot, store, schemas, headHash, chain },
   };
 }

packages/uwf-agent-kit/src/frontmatter.ts

@@ -0,0 +1,61 @@
+import { validate } from "@uncaged/json-cas";
+import type { Store } from "@uncaged/json-cas";
+import type { CasRef } from "@uncaged/uwf-protocol";
+import { parseFrontmatterMarkdown, validateFrontmatter } from "@uncaged/workflow-util";
+
+export type FrontmatterFastPathResult = {
+  body: string;
+  outputHash: CasRef;
+};
+
+/**
+ * Try to satisfy `outputSchema` from frontmatter fields alone.
+ *
+ * Returns a result containing the stored CAS hash and stripped body on success,
+ * or `null` when frontmatter is absent, invalid, or does not satisfy the schema.
+ * Never throws.
+ *
+ * The candidate object is put into the real CAS store (idempotent content-addressed
+ * write) and validated against the output schema.  If validation fails the node
+ * is orphaned — it will be GC'd on the next collection pass.
+ */
+export async function tryFrontmatterFastPath(
+  raw: string,
+  outputSchema: CasRef,
+  store: Store,
+): Promise<FrontmatterFastPathResult | null> {
+  const { frontmatter, body } = parseFrontmatterMarkdown(raw);
+
+  if (frontmatter === null) {
+    return null;
+  }
+
+  const validationErrors = validateFrontmatter(frontmatter);
+  if (validationErrors.length > 0) {
+    return null;
+  }
+
+  const candidate: Record<string, unknown> = {
+    status: frontmatter.status,
+    next: frontmatter.next,
+    confidence: frontmatter.confidence,
+    artifacts: [...frontmatter.artifacts],
+    scope: frontmatter.scope,
+  };
+
+  let outputHash: CasRef;
+  let node: ReturnType<Store["get"]>;
+
+  try {
+    outputHash = await store.put(outputSchema, candidate);
+    node = store.get(outputHash);
+  } catch {
+    return null;
+  }
+
+  if (node === null || !validate(store, node)) {
+    return null;
+  }
+
+  return { body, outputHash };
+}

packages/uwf-agent-kit/src/index.ts

@@ -6,6 +6,9 @@ export {
   resolveExtractModelAlias,
   resolveModel,
 } from "./extract.js";
+export { buildOutputFormatInstruction } from "./build-output-format-instruction.js";
+export type { FrontmatterFastPathResult } from "./frontmatter.js";
+export { tryFrontmatterFastPath } from "./frontmatter.js";
 export { createAgent } from "./run.js";
 export { getConfigPath, getEnvPath, loadWorkflowConfig } from "./storage.js";
 export type { AgentContext, AgentOptions, AgentRunFn, AgentRunResult } from "./types.js";

packages/uwf-agent-kit/src/run.ts

@@ -1,9 +1,11 @@
-import { validate } from "@uncaged/json-cas";
+import { getSchema, validate } from "@uncaged/json-cas";
 import type { CasRef, StepNodePayload, ThreadId } from "@uncaged/uwf-protocol";
 import { config as loadDotenv } from "dotenv";
 
 import { buildContextWithMeta } from "./context.js";
+import { buildOutputFormatInstruction } from "./build-output-format-instruction.js";
 import { extract } from "./extract.js";
+import { tryFrontmatterFastPath } from "./frontmatter.js";
 import type { AgentStore } from "./storage.js";
 import { getEnvPath, loadWorkflowConfig, resolveStorageRoot } from "./storage.js";
 import type { AgentContext, AgentOptions, AgentRunResult } from "./types.js";
@@ -73,7 +75,16 @@ async function extractOutput(
   rawOutput: string,
   outputSchema: CasRef,
   storageRoot: string,
+  ctx: Awaited<ReturnType<typeof buildContextWithMeta>>,
 ): Promise<CasRef> {
+  const fastPath = await runWithMessage("frontmatter fast path", () =>
+    tryFrontmatterFastPath(rawOutput, outputSchema, ctx.meta.store),
+  ).catch(() => null);
+
+  if (fastPath !== null) {
+    return fastPath.outputHash;
+  }
+
   const config = await runWithMessage("failed to load config", () =>
     loadWorkflowConfig(storageRoot),
   );
@@ -120,8 +131,13 @@ export function createAgent(options: AgentOptions): () => Promise<void> {
       fail(`unknown role: ${role}`);
     }
 
+    const outputSchema = getSchema(ctx.meta.store, roleDef.outputSchema);
+    if (outputSchema !== null) {
+      ctx.outputFormatInstruction = buildOutputFormatInstruction(outputSchema);
+    }
+
     const agentResult = await runAgent(options, ctx);
-    const outputHash = await extractOutput(agentResult.output, roleDef.outputSchema, storageRoot);
+    const outputHash = await extractOutput(agentResult.output, roleDef.outputSchema, storageRoot, ctx);
     const stepHash = await persistStep({
       ctx,
       outputHash,

packages/uwf-agent-kit/src/types.ts

@@ -6,6 +6,12 @@ export type AgentContext = ModeratorContext & {
   role: string;
   store: Store;
   workflow: WorkflowPayload;
+  /**
+   * Prepend to the role's systemPrompt when building the agent prompt.
+   * Contains the frontmatter deliverable format instruction derived from the
+   * role's output schema.  Populated by `createAgent` at run time.
+   */
+  outputFormatInstruction: string;
 };
 
 export type AgentRunResult = {

packages/workflow-util-agent/__tests__/build-output-format-instruction.test.ts

@@ -0,0 +1,80 @@
+import { describe, expect, test } from "vitest";
+import * as z from "zod/v4";
+
+import { buildOutputFormatInstruction } from "../src/build-output-format-instruction.js";
+
+describe("buildOutputFormatInstruction", () => {
+  test("always includes the frontmatter example block", () => {
+    const schema = z.object({ status: z.string() });
+    const result = buildOutputFormatInstruction(schema);
+    expect(result).toContain("## Deliverable Format");
+    expect(result).toContain("status:");
+    expect(result).toContain("confidence:");
+    expect(result).toContain("artifacts:");
+    expect(result).toContain("scope:");
+  });
+
+  test("always includes scope reminder", () => {
+    const schema = z.object({ status: z.string() });
+    const result = buildOutputFormatInstruction(schema);
+    expect(result).toContain("Focus exclusively on YOUR role's deliverable");
+    expect(result).toContain("Do not perform actions outside your role's scope");
+  });
+
+  test("lists fields from a flat ZodObject schema", () => {
+    const schema = z.object({
+      title: z.string(),
+      phases: z.array(z.string()),
+      reason: z.union([z.string(), z.null()]),
+    });
+    const result = buildOutputFormatInstruction(schema);
+    expect(result).toContain("`title`");
+    expect(result).toContain("`phases`");
+    expect(result).toContain("`reason`");
+  });
+
+  test("lists union of fields from a discriminated union schema", () => {
+    const schema = z.discriminatedUnion("status", [
+      z.object({ status: z.literal("planned"), phases: z.array(z.string()) }),
+      z.object({ status: z.literal("aborted"), reason: z.string() }),
+    ]);
+    const result = buildOutputFormatInstruction(schema);
+    expect(result).toContain("`status`");
+    expect(result).toContain("`phases`");
+    expect(result).toContain("`reason`");
+  });
+
+  test("lists fields from a plain ZodUnion schema", () => {
+    const schema = z.union([
+      z.object({ kind: z.literal("a"), valueA: z.string() }),
+      z.object({ kind: z.literal("b"), valueB: z.number() }),
+    ]);
+    const result = buildOutputFormatInstruction(schema);
+    expect(result).toContain("`kind`");
+    expect(result).toContain("`valueA`");
+    expect(result).toContain("`valueB`");
+  });
+
+  test("falls back gracefully for a non-object schema (no field list crash)", () => {
+    const schema = z.string();
+    const result = buildOutputFormatInstruction(schema);
+    expect(result).toContain("## Deliverable Format");
+    expect(result).toContain("schema fields will be extracted automatically");
+  });
+
+  test("marks frontmatter as the primary deliverable", () => {
+    const schema = z.object({ done: z.boolean() });
+    const result = buildOutputFormatInstruction(schema);
+    expect(result).toContain("primary deliverable");
+  });
+
+  test("no field is listed more than once for a union with overlapping keys", () => {
+    const schema = z.union([
+      z.object({ status: z.literal("a"), shared: z.string() }),
+      z.object({ status: z.literal("b"), shared: z.string() }),
+    ]);
+    const result = buildOutputFormatInstruction(schema);
+    const matches = [...result.matchAll(/`shared`/g)];
+    expect(matches.length).toBe(1);
+  });
+});

packages/workflow-util-agent/__tests__/create-agent-adapter.test.ts

@@ -0,0 +1,238 @@
+import { describe, expect, test, vi } from "vitest";
+
+const mock = vi.fn;
+
+import type { CasStore } from "@uncaged/workflow-cas";
+import type { ThreadContext, WorkflowRuntime } from "@uncaged/workflow-runtime";
+import * as z from "zod/v4";
+
+import { createAgentAdapter } from "../src/index.js";
+
+// ── Minimal test fixtures ─────────────────────────────────────────────────────
+
+function makeCtx(): ThreadContext {
+  return {
+    threadId: "01TEST000000000000000000TR",
+    depth: 0,
+    bundleHash: "TESTHASH00001",
+    start: {
+      role: "START" as const,
+      content: "test task",
+      meta: {},
+      timestamp: 1,
+      parentState: null,
+    },
+    steps: [],
+  };
+}
+
+function makeCas(): CasStore & { store: Map<string, string> } {
+  const store = new Map<string, string>();
+  let seq = 0;
+  return {
+    store,
+    async put(content: string) {
+      const hash = `HASH${String(++seq).padStart(9, "0")}`;
+      store.set(hash, content);
+      return hash;
+    },
+    async get(hash: string) {
+      return store.get(hash) ?? null;
+    },
+    async delete(hash: string) {
+      store.delete(hash);
+    },
+    async list() {
+      return [...store.keys()];
+    },
+  };
+}
+
+// ── Frontmatter-compatible schema ─────────────────────────────────────────────
+
+// Schema that maps directly to AgentFrontmatter fields so happy path works.
+const FrontmatterSchema = z.object({
+  status: z.union([
+    z.literal("done"),
+    z.literal("needs_input"),
+    z.literal("in_progress"),
+    z.literal("failed"),
+    z.null(),
+  ]),
+  next: z.union([z.string(), z.null()]),
+  confidence: z.union([z.number(), z.null()]),
+  artifacts: z.array(z.string()),
+  scope: z.union([z.literal("role"), z.literal("thread")]),
+});
+
+type FrontmatterMeta = z.infer<typeof FrontmatterSchema>;
+
+// ── Happy path ────────────────────────────────────────────────────────────────
+
+describe("createAgentAdapter — happy path (valid frontmatter satisfies schema)", () => {
+  test("returns meta from frontmatter without calling runtime.extract", async () => {
+    const cas = makeCas();
+    const extractMock = mock(async () => {
+      throw new Error("runtime.extract must not be called in happy path");
+    });
+    const runtime: WorkflowRuntime = { cas, extract: extractMock as WorkflowRuntime["extract"] };
+
+    const rawOutput = [
+      "---",
+      "status: done",
+      "next: reviewer",
+      "confidence: 0.9",
+      "artifacts: [src/foo.ts]",
+      "scope: role",
+      "---",
+      "",
+      "## Summary",
+      "Work is complete.",
+    ].join("\n");
+
+    const agentFn = mock(async (_ctx: ThreadContext, _opts: null) => rawOutput);
+    const extractOpts = mock(async () => null);
+
+    const adapter = createAgentAdapter<null>(agentFn, extractOpts);
+    const roleFn = adapter<FrontmatterMeta>("test prompt", FrontmatterSchema);
+    const result = await roleFn(makeCtx(), runtime);
+
+    // Meta must come from frontmatter
+    expect(result.meta.status).toBe("done");
+    expect(result.meta.next).toBe("reviewer");
+    expect(result.meta.confidence).toBe(0.9);
+    expect(result.meta.artifacts).toEqual(["src/foo.ts"]);
+    expect(result.meta.scope).toBe("role");
+    expect(result.childThread).toBeNull();
+
+    // LLM extract must NOT have been called
+    expect(extractMock).not.toHaveBeenCalled();
+
+    // CAS should store the body (without frontmatter) as the CAS node payload
+    const storedContent = [...cas.store.values()][0] ?? "";
+    expect(storedContent).toContain("## Summary");
+    expect(storedContent).toContain("Work is complete.");
+    // The frontmatter block itself must not appear in the stored payload
+    expect(storedContent).not.toContain("status: done\n");
+  });
+
+  test("body stored in CAS does not include the frontmatter block", async () => {
+    const cas = makeCas();
+    const runtime: WorkflowRuntime = {
+      cas,
+      extract: mock(async () => {
+        throw new Error("must not be called");
+      }) as WorkflowRuntime["extract"],
+    };
+
+    const rawOutput =
+      "---\nstatus: done\nnext: null\nconfidence: null\nscope: role\n---\n\nThe actual work content here.";
+
+    const adapter = createAgentAdapter<null>(
+      mock(async () => rawOutput),
+      mock(async () => null),
+    );
+    const roleFn = adapter<FrontmatterMeta>("prompt", FrontmatterSchema);
+    await roleFn(makeCtx(), runtime);
+
+    // CAS node wraps content as `payload: <body>`; check the payload contains only body
+    const stored = [...cas.store.values()][0] ?? "";
+    expect(stored).toContain("The actual work content here.");
+    // The frontmatter block must be stripped
+    expect(stored).not.toContain("status: done");
+  });
+});
+
+// ── Fallback path ─────────────────────────────────────────────────────────────
+
+describe("createAgentAdapter — fallback path (no frontmatter)", () => {
+  test("calls runtime.extract when output has no frontmatter block", async () => {
+    const cas = makeCas();
+    const expectedMeta: FrontmatterMeta = {
+      status: "done",
+      next: null,
+      confidence: null,
+      artifacts: [],
+      scope: "role",
+    };
+
+    const extractFn = mock(async (_schema: unknown, _hash: string) => ({
+      meta: expectedMeta as Record<string, unknown>,
+      contentPayload: "plain text output",
+      refs: [],
+    }));
+    const runtime: WorkflowRuntime = { cas, extract: extractFn as WorkflowRuntime["extract"] };
+
+    const rawOutput = "This is plain markdown without any frontmatter.";
+    const adapter = createAgentAdapter<null>(
+      mock(async () => rawOutput),
+      mock(async () => null),
+    );
+    const roleFn = adapter<FrontmatterMeta>("prompt", FrontmatterSchema);
+    const result = await roleFn(makeCtx(), runtime);
+
+    // runtime.extract must have been called once
+    expect(extractFn).toHaveBeenCalledTimes(1);
+    expect(result.meta).toEqual(expectedMeta);
+    expect(result.childThread).toBeNull();
+
+    // CAS should store the full raw output (as CAS node payload)
+    const stored = [...cas.store.values()][0] ?? "";
+    expect(stored).toContain(rawOutput);
+  });
+
+  test("falls back to runtime.extract when frontmatter is structurally invalid", async () => {
+    const cas = makeCas();
+    const expectedMeta: FrontmatterMeta = {
+      status: null,
+      next: null,
+      confidence: null,
+      artifacts: [],
+      scope: "role",
+    };
+    const extractFn = mock(async () => ({
+      meta: expectedMeta as Record<string, unknown>,
+      contentPayload: "",
+      refs: [],
+    }));
+    const runtime: WorkflowRuntime = { cas, extract: extractFn as WorkflowRuntime["extract"] };
+
+    // confidence out of range — validateFrontmatter will reject
+    const rawOutput = "---\nstatus: done\nconfidence: 1.5\nscope: role\n---\n\nBody.";
+    const adapter = createAgentAdapter<null>(
+      mock(async () => rawOutput),
+      mock(async () => null),
+    );
+    const roleFn = adapter<FrontmatterMeta>("prompt", FrontmatterSchema);
+    await roleFn(makeCtx(), runtime);
+
+    expect(extractFn).toHaveBeenCalledTimes(1);
+  });
+
+  test("falls back when frontmatter fields do not satisfy schema", async () => {
+    const cas = makeCas();
+
+    // Schema requires a mandatory non-null string field that frontmatter cannot provide
+    const StrictSchema = z.object({
+      requiredField: z.string(),
+    });
+
+    const extractFn = mock(async () => ({
+      meta: { requiredField: "from-llm" } as Record<string, unknown>,
+      contentPayload: "",
+      refs: [],
+    }));
+    const runtime: WorkflowRuntime = { cas, extract: extractFn as WorkflowRuntime["extract"] };
+
+    const rawOutput = "---\nstatus: done\nscope: role\n---\n\nBody.";
+    const adapter = createAgentAdapter<null>(
+      mock(async () => rawOutput),
+      mock(async () => null),
+    );
+    const roleFn = adapter<{ requiredField: string }>("prompt", StrictSchema);
+    await roleFn(makeCtx(), runtime);
+
+    // frontmatter has no `requiredField`, so schema parse fails → fallback
+    expect(extractFn).toHaveBeenCalledTimes(1);
+  });
+});

packages/workflow-util-agent/package.json

@@ -21,6 +21,7 @@
   "dependencies": {
     "@uncaged/workflow-runtime": "workspace:^",
     "@uncaged/workflow-cas": "workspace:^",
+    "@uncaged/workflow-util": "workspace:^",
     "zod": "^4.0.0"
   },
   "publishConfig": {

packages/workflow-util-agent/src/build-agent-prompt.ts

@@ -3,30 +3,20 @@ import type { AgentContext, ThreadContext } from "@uncaged/workflow-runtime";
 /**
  * Builds a user-message string from thread context: task, previous steps, and tool hints.
  * Does NOT include a system prompt — that is passed separately via the adapter.
+ *
+ * Ordering: Task → Previous Steps → Parent Context → Tools
+ * The "Deliverable" section lives in the system prompt (injected by createAgentAdapter).
  */
 export async function buildThreadInput(ctx: ThreadContext): Promise<string> {
   const lines: string[] = [];
 
-  if (ctx.start.parentState !== null) {
-    lines.push("## Parent Context");
-    lines.push(
-      "This workflow was spawned by a parent workflow. The parent's state at spawn time is available at hash: " +
-        ctx.start.parentState,
-    );
-    lines.push(
-      `Use \`uncaged-workflow cas get ${ctx.start.parentState}\` to inspect the parent's context and trace back through its steps.`,
-    );
-    lines.push("");
-  }
-
+  // 1. Task — what to do
   lines.push("## Task");
   lines.push(ctx.start.content);
 
   const { steps } = ctx;
-  if (steps.length === 0) {
-    return lines.join("\n");
-  }
 
+  // 2. Context — previous steps
   if (steps.length === 1) {
     const s = steps[0];
     lines.push("");
@@ -34,7 +24,7 @@ export async function buildThreadInput(ctx: ThreadContext): Promise<string> {
     lines.push("");
     lines.push(`ContentHash: ${s.contentHash}`);
     lines.push(`Meta: ${JSON.stringify(s.meta)}`);
-  } else {
+  } else if (steps.length > 1) {
     lines.push("");
     lines.push("## Previous Steps");
     for (let i = 0; i < steps.length - 1; i++) {
@@ -51,6 +41,24 @@ export async function buildThreadInput(ctx: ThreadContext): Promise<string> {
     lines.push(`Meta: ${JSON.stringify(last.meta)}`);
   }
 
+  // 3. Parent context — available when this workflow was spawned by another
+  if (ctx.start.parentState !== null) {
+    lines.push("");
+    lines.push("## Parent Context");
+    lines.push(
+      "This workflow was spawned by a parent workflow. The parent's state at spawn time is available at hash: " +
+        ctx.start.parentState,
+    );
+    lines.push(
+      `Use \`uncaged-workflow cas get ${ctx.start.parentState}\` to inspect the parent's context and trace back through its steps.`,
+    );
+  }
+
+  if (steps.length === 0 && ctx.start.parentState === null) {
+    return lines.join("\n");
+  }
+
+  // 4. Tools — available commands
   lines.push("");
   lines.push("## Tools");
   lines.push(

packages/workflow-util-agent/src/build-output-format-instruction.ts

@@ -0,0 +1,79 @@
+import type * as z from "zod/v4";
+
+type ZodSchema = z.ZodType;
+
+/**
+ * Extract the top-level field names from a Zod schema.
+ *
+ * Handles:
+ * - ZodObject → its `.shape` keys
+ * - ZodDiscriminatedUnion / ZodUnion → union of all variant shapes
+ *
+ * Returns an empty array for schemas that have no inspectable shape
+ * (e.g. primitives, ZodAny).
+ */
+function extractSchemaFields(schema: ZodSchema): string[] {
+  const def = schema.def as {
+    type: string;
+    shape?: Record<string, ZodSchema>;
+    options?: ZodSchema[];
+  };
+
+  if (def.type === "object" && def.shape !== undefined) {
+    return Object.keys(def.shape);
+  }
+
+  if ((def.type === "discriminated_union" || def.type === "union") && Array.isArray(def.options)) {
+    const fieldSet = new Set<string>();
+    for (const option of def.options) {
+      for (const field of extractSchemaFields(option as ZodSchema)) {
+        fieldSet.add(field);
+      }
+    }
+    return [...fieldSet];
+  }
+
+  return [];
+}
+
+/**
+ * Build a concise output format instruction block for an agent role.
+ *
+ * The instruction describes the expected frontmatter markdown format and lists
+ * the meta fields derived from `schema`. It is injected at the top of the
+ * system prompt so the deliverable format is the first thing the agent sees.
+ *
+ * Focus on YOUR role's deliverable. Do not perform actions outside your role's scope.
+ */
+export function buildOutputFormatInstruction(schema: ZodSchema): string {
+  const fields = extractSchemaFields(schema);
+
+  const fieldList =
+    fields.length > 0
+      ? fields.map((f) => `  - \`${f}\``).join("\n")
+      : "  (schema fields will be extracted automatically)";
+
+  return `## Deliverable Format
+
+Your response MUST begin with a YAML frontmatter block followed by your markdown work:
+
+\`\`\`
+---
+status: done          # done | needs_input | in_progress | failed
+next: <role-name>     # suggested next role, or omit
+confidence: 0.9       # 0.0–1.0, your self-assessed confidence
+artifacts:            # list of file paths or CAS hashes you produced
+  - path/to/file.ts
+scope: role           # role | thread
+---
+
+... your markdown work here ...
+\`\`\`
+
+The frontmatter is the **primary deliverable** — the engine reads it directly.
+Your meta output must satisfy these fields:
+
+${fieldList}
+
+Focus exclusively on YOUR role's deliverable. Do not perform actions outside your role's scope.`;
+}

packages/workflow-util-agent/src/create-agent-adapter.ts

@@ -6,7 +6,15 @@ import type {
   ThreadContext,
   WorkflowRuntime,
 } from "@uncaged/workflow-runtime";
+import {
+  createLogger,
+  parseFrontmatterMarkdown,
+  validateFrontmatter,
+} from "@uncaged/workflow-util";
 import type * as z from "zod/v4";
+import { buildOutputFormatInstruction } from "./build-output-format-instruction.js";
+
+const log = createLogger({ sink: { kind: "stderr" } });
 
 export type ExtractOptionsFn<Opt> = (
   ctx: ThreadContext,
@@ -14,22 +22,82 @@ export type ExtractOptionsFn<Opt> = (
   runtime: WorkflowRuntime,
 ) => Promise<Opt>;
 
+/**
+ * Try to satisfy `schema` from frontmatter fields alone.
+ *
+ * Returns the parsed value on success, or `null` when the frontmatter does not
+ * cover all required fields of the schema.  Never throws.
+ */
+function tryFrontmatterMeta<T>(
+  raw: string,
+  schema: z.ZodType<T>,
+): { meta: T; body: string } | null {
+  const { frontmatter, body } = parseFrontmatterMarkdown(raw);
+
+  if (frontmatter === null) {
+    return null;
+  }
+
+  const validationErrors = validateFrontmatter(frontmatter);
+  if (validationErrors.length > 0) {
+    log(
+      "4KNMR2PX",
+      `frontmatter validation errors: ${validationErrors.map((e) => e.message).join("; ")}`,
+    );
+    return null;
+  }
+
+  // Coerce frontmatter into the plain object shape the schema expects.
+  const candidate: Record<string, unknown> = {
+    status: frontmatter.status,
+    next: frontmatter.next,
+    confidence: frontmatter.confidence,
+    artifacts: frontmatter.artifacts,
+    scope: frontmatter.scope,
+  };
+
+  const result = schema.safeParse(candidate);
+  if (!result.success) {
+    log("7BQST3VW", "frontmatter does not satisfy schema; falling back to extract");
+    return null;
+  }
+
+  return { meta: result.data, body };
+}
+
 /**
  * Bridges {@link AgentFn} to {@link AdapterFn}.
  *
- * 1. extract(ctx, prompt, runtime) → Opt
- * 2. agent(ctx, options) → raw string
- * 3. Store raw string in CAS
- * 4. runtime.extract(schema, contentHash) → typed meta T
+ * Happy path (zero LLM cost):
+ *   1. extract(ctx, prompt, runtime) → Opt
+ *   2. agent(ctx, options) → raw string
+ *   3. Parse raw as frontmatter markdown
+ *   4. If frontmatter is valid AND satisfies `schema` → use as meta directly
+ *      CAS stores the body (without frontmatter block)
+ *
+ * Fallback (safety net):
+ *   4b. Store full raw in CAS
+ *   5b. runtime.extract(schema, contentHash) → typed meta via LLM
  */
 export function createAgentAdapter<Opt>(
   agent: AgentFn<Opt>,
   extract: ExtractOptionsFn<Opt>,
 ): AdapterFn {
   return <T>(prompt: string, schema: z.ZodType<T>) => {
+    const augmentedPrompt = `${buildOutputFormatInstruction(schema)}\n\n${prompt}`;
     return async (ctx: ThreadContext, runtime: WorkflowRuntime): Promise<RoleResult<T>> => {
-      const options = await extract(ctx, prompt, runtime);
+      const options = await extract(ctx, augmentedPrompt, runtime);
       const raw = await agent(ctx, options);
+
+      const frontmatterResult = tryFrontmatterMeta(raw, schema);
+
+      if (frontmatterResult !== null) {
+        log("3VXPW8QR", "frontmatter satisfied schema — skipping LLM extract");
+        await putContentNodeWithRefs(runtime.cas, frontmatterResult.body, []);
+        return { meta: frontmatterResult.meta, childThread: null };
+      }
+
+      log("8MTNJ5YK", "no valid frontmatter — falling back to runtime.extract");
       const contentHash = await putContentNodeWithRefs(runtime.cas, raw, []);
       const extracted = await runtime.extract(
         schema as z.ZodType<Record<string, unknown>>,

packages/workflow-util-agent/src/index.ts

@@ -1,4 +1,5 @@
 export { buildAgentPrompt, buildThreadInput } from "./build-agent-prompt.js";
+export { buildOutputFormatInstruction } from "./build-output-format-instruction.js";
 export { createAgentAdapter } from "./create-agent-adapter.js";
 export type { SpawnCliError } from "./spawn-cli.js";
 export { spawnCli } from "./spawn-cli.js";

packages/workflow-util/__tests__/frontmatter-markdown.test.ts

@@ -0,0 +1,343 @@
+import { describe, expect, it } from "vitest";
+import type { AgentFrontmatter } from "../src/index.js";
+import { parseFrontmatterMarkdown, validateFrontmatter } from "../src/index.js";
+
+// ── parseFrontmatterMarkdown ─────────────────────────────────────────────────
+
+describe("parseFrontmatterMarkdown", () => {
+  describe("no frontmatter", () => {
+    it("returns null frontmatter and full text as body when no fence", () => {
+      const raw = "Just some markdown text.\n\n## Section\n\nContent.";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.frontmatter).toBeNull();
+      expect(result.body).toBe(raw);
+    });
+
+    it("returns null frontmatter when --- appears mid-document", () => {
+      const raw = "# Heading\n\n---\n\nContent.";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.frontmatter).toBeNull();
+      expect(result.body).toBe(raw);
+    });
+
+    it("returns null frontmatter when opening fence is not followed by newline", () => {
+      const raw = "--- inline content ---\nbody";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.frontmatter).toBeNull();
+      expect(result.body).toBe(raw);
+    });
+
+    it("returns null frontmatter when no closing fence", () => {
+      const raw = "---\nstatus: done\nbody without close";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.frontmatter).toBeNull();
+      expect(result.body).toBe(raw);
+    });
+
+    it("handles empty string", () => {
+      const result = parseFrontmatterMarkdown("");
+      expect(result.frontmatter).toBeNull();
+      expect(result.body).toBe("");
+    });
+  });
+
+  describe("full frontmatter document", () => {
+    it("parses all fields from a well-formed document", () => {
+      const raw = `---
+status: done
+next: reviewer
+confidence: 0.9
+artifacts:
+  - src/foo.ts
+  - src/bar.ts
+scope: thread
+---
+
+## Summary
+
+Everything looks good.`;
+
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.frontmatter).not.toBeNull();
+      const fm = result.frontmatter!;
+      expect(fm.status).toBe("done");
+      expect(fm.next).toBe("reviewer");
+      expect(fm.confidence).toBe(0.9);
+      expect(fm.artifacts).toEqual(["src/foo.ts", "src/bar.ts"]);
+      expect(fm.scope).toBe("thread");
+      expect(result.body).toBe("## Summary\n\nEverything looks good.");
+    });
+
+    it("strips leading newline from body", () => {
+      const raw = "---\nstatus: done\n---\n\nbody here";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.body).toBe("body here");
+    });
+
+    it("body is empty string when nothing after closing fence", () => {
+      const raw = "---\nstatus: done\n---\n";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.body).toBe("");
+    });
+
+    it("body is empty string when document ends exactly at closing fence", () => {
+      const raw = "---\nstatus: done\n---";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.body).toBe("");
+    });
+  });
+
+  describe("status field", () => {
+    it.each([
+      "done",
+      "needs_input",
+      "in_progress",
+      "failed",
+    ] as const)('parses status "%s"', (status) => {
+      const raw = `---\nstatus: ${status}\n---\nbody`;
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.frontmatter?.status).toBe(status);
+    });
+
+    it("returns null status for unknown value", () => {
+      const raw = "---\nstatus: unknown_value\n---\nbody";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.frontmatter?.status).toBeNull();
+    });
+
+    it("returns null status when omitted", () => {
+      const raw = "---\nconfidence: 0.5\n---\nbody";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.frontmatter?.status).toBeNull();
+    });
+  });
+
+  describe("confidence field", () => {
+    it("parses integer as number", () => {
+      const raw = "---\nconfidence: 1\n---\nbody";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.frontmatter?.confidence).toBe(1);
+    });
+
+    it("parses decimal", () => {
+      const raw = "---\nconfidence: 0.75\n---\nbody";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.frontmatter?.confidence).toBe(0.75);
+    });
+
+    it("returns null when omitted", () => {
+      const raw = "---\nstatus: done\n---\nbody";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.frontmatter?.confidence).toBeNull();
+    });
+
+    it("returns null for non-numeric value", () => {
+      const raw = "---\nconfidence: high\n---\nbody";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.frontmatter?.confidence).toBeNull();
+    });
+  });
+
+  describe("artifacts field", () => {
+    it("parses block sequence", () => {
+      const raw = "---\nartifacts:\n  - a.ts\n  - b.ts\n---\nbody";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.frontmatter?.artifacts).toEqual(["a.ts", "b.ts"]);
+    });
+
+    it("parses inline sequence", () => {
+      const raw = "---\nartifacts: [a.ts, b.ts]\n---\nbody";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.frontmatter?.artifacts).toEqual(["a.ts", "b.ts"]);
+    });
+
+    it("returns empty array when omitted", () => {
+      const raw = "---\nstatus: done\n---\nbody";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.frontmatter?.artifacts).toEqual([]);
+    });
+
+    it("wraps single scalar in array", () => {
+      const raw = "---\nartifacts: only-one.ts\n---\nbody";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.frontmatter?.artifacts).toEqual(["only-one.ts"]);
+    });
+  });
+
+  describe("scope field", () => {
+    it('parses scope "role"', () => {
+      const raw = "---\nscope: role\n---\nbody";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.frontmatter?.scope).toBe("role");
+    });
+
+    it('parses scope "thread"', () => {
+      const raw = "---\nscope: thread\n---\nbody";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.frontmatter?.scope).toBe("thread");
+    });
+
+    it('defaults to "role" when omitted', () => {
+      const raw = "---\nstatus: done\n---\nbody";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.frontmatter?.scope).toBe("role");
+    });
+
+    it('defaults to "role" for unknown scope value', () => {
+      const raw = "---\nscope: global\n---\nbody";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.frontmatter?.scope).toBe("role");
+    });
+  });
+
+  describe("next field", () => {
+    it("parses a role name", () => {
+      const raw = "---\nnext: planner\n---\nbody";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.frontmatter?.next).toBe("planner");
+    });
+
+    it("returns null when omitted", () => {
+      const raw = "---\nstatus: done\n---\nbody";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.frontmatter?.next).toBeNull();
+    });
+  });
+
+  describe("unknown fields", () => {
+    it("ignores unknown keys silently", () => {
+      const raw = "---\nunknown_field: some_value\nstatus: done\n---\nbody";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.frontmatter?.status).toBe("done");
+    });
+  });
+
+  describe("YAML comments", () => {
+    it("ignores YAML comment lines", () => {
+      const raw = "---\n# this is a comment\nstatus: done\n---\nbody";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.frontmatter?.status).toBe("done");
+    });
+  });
+
+  describe("empty frontmatter block", () => {
+    it("parses empty frontmatter and uses all defaults", () => {
+      const raw = "---\n---\nbody";
+      const result = parseFrontmatterMarkdown(raw);
+      expect(result.frontmatter).not.toBeNull();
+      const fm = result.frontmatter!;
+      expect(fm.status).toBeNull();
+      expect(fm.next).toBeNull();
+      expect(fm.confidence).toBeNull();
+      expect(fm.artifacts).toEqual([]);
+      expect(fm.scope).toBe("role");
+      expect(result.body).toBe("body");
+    });
+  });
+});
+
+// ── validateFrontmatter ──────────────────────────────────────────────────────
+
+function validFm(overrides: Partial<AgentFrontmatter> = {}): AgentFrontmatter {
+  return {
+    status: "done",
+    next: null,
+    confidence: null,
+    artifacts: [],
+    scope: "role",
+    ...overrides,
+  };
+}
+
+describe("validateFrontmatter", () => {
+  it("returns no errors for a fully valid frontmatter", () => {
+    const errors = validateFrontmatter(validFm());
+    expect(errors).toHaveLength(0);
+  });
+
+  it("returns no errors when all nullable fields are null", () => {
+    const fm: AgentFrontmatter = {
+      status: null,
+      next: null,
+      confidence: null,
+      artifacts: [],
+      scope: "role",
+    };
+    expect(validateFrontmatter(fm)).toHaveLength(0);
+  });
+
+  describe("confidence validation", () => {
+    it("accepts 0.0", () => {
+      expect(validateFrontmatter(validFm({ confidence: 0 }))).toHaveLength(0);
+    });
+
+    it("accepts 1.0", () => {
+      expect(validateFrontmatter(validFm({ confidence: 1 }))).toHaveLength(0);
+    });
+
+    it("rejects value below 0", () => {
+      const errors = validateFrontmatter(validFm({ confidence: -0.1 }));
+      expect(errors).toHaveLength(1);
+      expect(errors[0]?.field).toBe("confidence");
+    });
+
+    it("rejects value above 1", () => {
+      const errors = validateFrontmatter(validFm({ confidence: 1.01 }));
+      expect(errors).toHaveLength(1);
+      expect(errors[0]?.field).toBe("confidence");
+    });
+  });
+
+  describe("next validation", () => {
+    it("accepts a simple role name", () => {
+      expect(validateFrontmatter(validFm({ next: "reviewer" }))).toHaveLength(0);
+    });
+
+    it("accepts kebab-case role name", () => {
+      expect(validateFrontmatter(validFm({ next: "code-reviewer" }))).toHaveLength(0);
+    });
+
+    it("rejects role name with whitespace", () => {
+      const errors = validateFrontmatter(validFm({ next: "role name" }));
+      expect(errors).toHaveLength(1);
+      expect(errors[0]?.field).toBe("next");
+    });
+  });
+
+  describe("artifacts validation", () => {
+    it("accepts non-empty path strings", () => {
+      expect(
+        validateFrontmatter(validFm({ artifacts: ["src/foo.ts", "src/bar.ts"] })),
+      ).toHaveLength(0);
+    });
+
+    it("rejects empty string artifact entries", () => {
+      const errors = validateFrontmatter(validFm({ artifacts: [""] }));
+      expect(errors).toHaveLength(1);
+      expect(errors[0]?.field).toBe("artifacts");
+    });
+
+    it("rejects whitespace-only artifact entries", () => {
+      const errors = validateFrontmatter(validFm({ artifacts: ["   "] }));
+      expect(errors).toHaveLength(1);
+      expect(errors[0]?.field).toBe("artifacts");
+    });
+  });
+
+  describe("multiple errors", () => {
+    it("reports multiple violations at once", () => {
+      const fm: AgentFrontmatter = {
+        status: "done",
+        next: "bad role",
+        confidence: 2,
+        artifacts: [""],
+        scope: "role",
+      };
+      const errors = validateFrontmatter(fm);
+      const fields = errors.map((e) => e.field);
+      expect(fields).toContain("next");
+      expect(fields).toContain("confidence");
+      expect(fields).toContain("artifacts");
+    });
+  });
+});

packages/workflow-util/src/frontmatter-markdown/frontmatter-markdown.ts

@@ -0,0 +1,291 @@
+import type {
+  AgentFrontmatter,
+  FrontmatterScope,
+  FrontmatterStatus,
+  FrontmatterValidationError,
+  ParsedFrontmatterMarkdown,
+} from "./types.js";
+
+// ── YAML frontmatter extractor ───────────────────────────────────────────────
+
+const FENCE = "---";
+
+/**
+ * Split a raw agent response into a YAML string (or null) and a markdown body.
+ *
+ * A frontmatter block MUST:
+ *   1. Start at character position 0 with `---` (no leading whitespace / BOM).
+ *   2. Be closed by a second `---` on its own line.
+ *
+ * Anything that doesn't match this shape is returned verbatim as the body.
+ */
+function splitFrontmatter(raw: string): { yaml: string | null; body: string } {
+  if (!raw.startsWith(FENCE)) {
+    return { yaml: null, body: raw };
+  }
+
+  const rest = raw.slice(FENCE.length);
+  // The opening `---` must be followed immediately by a newline (or end-of-string).
+  if (rest.length > 0 && rest[0] !== "\n" && rest[0] !== "\r") {
+    return { yaml: null, body: raw };
+  }
+  // Consume the newline after the opening fence so that `afterOpen` starts at the
+  // first line of YAML content (not a leading empty line).
+  const afterOpen = rest.startsWith("\n") ? rest.slice(1) : rest;
+
+  const closeIndex = afterOpen.indexOf(`\n${FENCE}`);
+  if (closeIndex === -1) {
+    // Also handle the edge case where frontmatter is empty: `---\n---`
+    if (afterOpen.startsWith(FENCE)) {
+      const afterClose = afterOpen.slice(FENCE.length);
+      const body = afterClose.replace(/^\n+/, "");
+      return { yaml: "", body };
+    }
+    return { yaml: null, body: raw };
+  }
+
+  const yaml = afterOpen.slice(0, closeIndex);
+  // Skip past `\n---` and strip any leading blank separator lines from the body.
+  const afterClose = afterOpen.slice(closeIndex + 1 + FENCE.length);
+  const body = afterClose.replace(/^\n+/, "");
+
+  return { yaml, body };
+}
+
+// ── Minimal YAML scalar parser ───────────────────────────────────────────────
+//
+// We intentionally avoid a full YAML library dependency inside workflow-util.
+// The frontmatter schema is flat and uses only scalars + simple string lists.
+// This parser handles exactly what the spec needs and nothing more.
+
+type YamlValue = string | number | boolean | null | string[];
+
+function parseYamlScalar(raw: string): YamlValue {
+  const trimmed = raw.trim();
+
+  // Quoted string
+  if (
+    (trimmed.startsWith('"') && trimmed.endsWith('"')) ||
+    (trimmed.startsWith("'") && trimmed.endsWith("'"))
+  ) {
+    return trimmed.slice(1, -1);
+  }
+
+  const lower = trimmed.toLowerCase();
+  if (lower === "true") return true;
+  if (lower === "false") return false;
+  if (lower === "null" || lower === "~" || lower === "") return null;
+
+  const num = Number(trimmed);
+  if (!Number.isNaN(num) && trimmed !== "") return num;
+
+  return trimmed;
+}
+
+function collectBlockSequence(
+  lines: string[],
+  startIdx: number,
+): { items: string[]; nextIdx: number } {
+  const items: string[] = [];
+  let i = startIdx;
+  while (i < lines.length) {
+    const itemTrimmed = (lines[i] ?? "").trimStart();
+    if (!itemTrimmed.startsWith("- ")) break;
+    items.push(itemTrimmed.slice(2).trim());
+    i++;
+  }
+  return { items, nextIdx: i };
+}
+
+function parseInlineSequence(restTrimmed: string): string[] {
+  const inner = restTrimmed.slice(1, -1);
+  return inner
+    .split(",")
+    .map((s) => s.trim())
+    .filter((s) => s !== "");
+}
+
+function parseKeyValue(
+  lines: string[],
+  i: number,
+): { key: string; value: YamlValue; nextIdx: number } | null {
+  const line = lines[i] ?? "";
+  if (line.trim() === "" || line.trimStart().startsWith("#")) {
+    return null;
+  }
+  const colonIdx = line.indexOf(":");
+  if (colonIdx === -1) {
+    return null;
+  }
+  const key = line.slice(0, colonIdx).trim();
+  const restTrimmed = line.slice(colonIdx + 1).trim();
+
+  if (restTrimmed === "") {
+    const { items, nextIdx } = collectBlockSequence(lines, i + 1);
+    return { key, value: items, nextIdx };
+  }
+  if (restTrimmed.startsWith("[") && restTrimmed.endsWith("]")) {
+    return { key, value: parseInlineSequence(restTrimmed), nextIdx: i + 1 };
+  }
+  return { key, value: parseYamlScalar(restTrimmed), nextIdx: i + 1 };
+}
+
+/**
+ * Parse a minimal flat YAML document.  Only supports:
+ * - Scalar key: value pairs
+ * - Block sequences under a key (items prefixed with `  - `)
+ *
+ * Returns a plain object.  Never throws — unparseable lines are silently skipped.
+ */
+function parseMinimalYaml(yaml: string): Record<string, YamlValue> {
+  const result: Record<string, YamlValue> = {};
+  const lines = yaml.split("\n");
+
+  let i = 0;
+  while (i < lines.length) {
+    const entry = parseKeyValue(lines, i);
+    if (entry === null) {
+      i++;
+      continue;
+    }
+    result[entry.key] = entry.value;
+    i = entry.nextIdx;
+  }
+
+  return result;
+}
+
+// ── Field coercers ───────────────────────────────────────────────────────────
+
+const VALID_STATUS: readonly FrontmatterStatus[] = ["done", "needs_input", "in_progress", "failed"];
+
+const VALID_SCOPE: readonly FrontmatterScope[] = ["role", "thread"];
+
+function coerceStatus(raw: YamlValue): FrontmatterStatus | null {
+  if (raw === null || raw === undefined) return null;
+  const s = String(raw).trim().toLowerCase();
+  return VALID_STATUS.includes(s as FrontmatterStatus) ? (s as FrontmatterStatus) : null;
+}
+
+function coerceNext(raw: YamlValue): string | null {
+  if (raw === null || raw === undefined) return null;
+  const s = String(raw).trim();
+  return s === "" ? null : s;
+}
+
+function coerceConfidence(raw: YamlValue): number | null {
+  if (raw === null || raw === undefined) return null;
+  const n = typeof raw === "number" ? raw : Number(String(raw).trim());
+  if (Number.isNaN(n)) return null;
+  return n;
+}
+
+function coerceArtifacts(raw: YamlValue): readonly string[] {
+  if (raw === null || raw === undefined) return [];
+  if (Array.isArray(raw)) return raw.map(String).filter((s) => s !== "");
+  const s = String(raw).trim();
+  return s === "" ? [] : [s];
+}
+
+function coerceScope(raw: YamlValue): FrontmatterScope {
+  if (raw === null || raw === undefined) return "role";
+  const s = String(raw).trim().toLowerCase();
+  return VALID_SCOPE.includes(s as FrontmatterScope) ? (s as FrontmatterScope) : "role";
+}
+
+// ── Public API ───────────────────────────────────────────────────────────────
+
+/**
+ * Parse a raw agent response string into structured frontmatter + body.
+ *
+ * - Never throws: malformed YAML is silently treated as "no frontmatter".
+ * - The returned `frontmatter` is `null` when no valid `---…---` block was found.
+ * - Unknown YAML keys are silently ignored.
+ * - Invalid scalar values for known keys are coerced to their null/default.
+ */
+export function parseFrontmatterMarkdown(raw: string): ParsedFrontmatterMarkdown {
+  const { yaml, body } = splitFrontmatter(raw);
+
+  if (yaml === null) {
+    return { frontmatter: null, body };
+  }
+
+  let fields: Record<string, YamlValue>;
+  try {
+    fields = parseMinimalYaml(yaml);
+  } catch {
+    // Unparseable YAML → treat as no frontmatter; keep full raw as body.
+    return { frontmatter: null, body: raw };
+  }
+
+  const frontmatter: AgentFrontmatter = {
+    status: coerceStatus(fields.status ?? null),
+    next: coerceNext(fields.next ?? null),
+    confidence: coerceConfidence(fields.confidence ?? null),
+    artifacts: coerceArtifacts(fields.artifacts ?? null),
+    scope: coerceScope(fields.scope ?? null),
+  };
+
+  return { frontmatter, body };
+}
+
+/**
+ * Validate a parsed `AgentFrontmatter` and return a list of violations.
+ *
+ * An empty array means the frontmatter is valid.
+ *
+ * Validated constraints:
+ * - `status`     — must be one of the FrontmatterStatus literals (if non-null)
+ * - `confidence` — must be in [0.0, 1.0] (if non-null)
+ * - `next`       — must be a non-empty string with no whitespace (if non-null)
+ * - `artifacts`  — each entry must be a non-empty string
+ * - `scope`      — must be one of the FrontmatterScope literals
+ */
+export function validateFrontmatter(
+  frontmatter: AgentFrontmatter,
+): readonly FrontmatterValidationError[] {
+  const errors: FrontmatterValidationError[] = [];
+
+  if (frontmatter.status !== null && !VALID_STATUS.includes(frontmatter.status)) {
+    errors.push({
+      field: "status",
+      message: `invalid status "${frontmatter.status}"; must be one of: ${VALID_STATUS.join(", ")}`,
+    });
+  }
+
+  if (frontmatter.confidence !== null) {
+    if (frontmatter.confidence < 0 || frontmatter.confidence > 1) {
+      errors.push({
+        field: "confidence",
+        message: `confidence ${frontmatter.confidence} is out of range; must be between 0.0 and 1.0 inclusive`,
+      });
+    }
+  }
+
+  if (frontmatter.next !== null) {
+    if (frontmatter.next.trim() === "") {
+      errors.push({ field: "next", message: "next must be a non-empty string when present" });
+    } else if (/\s/.test(frontmatter.next)) {
+      errors.push({
+        field: "next",
+        message: `next "${frontmatter.next}" must not contain whitespace`,
+      });
+    }
+  }
+
+  for (const artifact of frontmatter.artifacts) {
+    if (artifact.trim() === "") {
+      errors.push({ field: "artifacts", message: "artifact entries must be non-empty strings" });
+      break;
+    }
+  }
+
+  if (!VALID_SCOPE.includes(frontmatter.scope)) {
+    errors.push({
+      field: "scope",
+      message: `invalid scope "${frontmatter.scope}"; must be one of: ${VALID_SCOPE.join(", ")}`,
+    });
+  }
+
+  return errors;
+}

packages/workflow-util/src/frontmatter-markdown/index.ts

@@ -0,0 +1,8 @@
+export { parseFrontmatterMarkdown, validateFrontmatter } from "./frontmatter-markdown.js";
+export type {
+  AgentFrontmatter,
+  FrontmatterScope,
+  FrontmatterStatus,
+  FrontmatterValidationError,
+  ParsedFrontmatterMarkdown,
+} from "./types.js";

packages/workflow-util/src/frontmatter-markdown/types.ts

@@ -0,0 +1,111 @@
+/**
+ * Frontmatter Markdown — agent output format (RFC #351 Phase 1).
+ *
+ * An agent response is a Markdown document with an optional YAML frontmatter
+ * block at the top.  The frontmatter carries structured signals that the
+ * moderator and engine can consume without running a full LLM extract pass.
+ *
+ * Wire format:
+ *
+ *   ---
+ *   status: done
+ *   next: reviewer
+ *   confidence: 0.9
+ *   artifacts:
+ *     - src/foo.ts
+ *   scope: role
+ *   ---
+ *
+ *   ... free-form markdown body ...
+ *
+ * All frontmatter fields are optional at the parse level.  `validateFrontmatter`
+ * enforces the constraints documented on each field below.
+ */
+
+// ── Vocabulary types ─────────────────────────────────────────────────────────
+
+/**
+ * High-level signal from the agent about where work stands.
+ *
+ * - `done`        — role completed its objective; moderator may advance
+ * - `needs_input` — agent is blocked and requires human or peer clarification
+ * - `in_progress` — work is underway but the agent chose to yield early
+ * - `failed`      — agent cannot complete the task and explains why in the body
+ */
+export type FrontmatterStatus = "done" | "needs_input" | "in_progress" | "failed";
+
+/**
+ * Scope of frontmatter signals.
+ *
+ * - `role`   — signals apply to the current role execution only (default)
+ * - `thread` — signals are suggestions for the entire thread moderator
+ */
+export type FrontmatterScope = "role" | "thread";
+
+// ── Core frontmatter schema ──────────────────────────────────────────────────
+
+/**
+ * Parsed and validated frontmatter from an agent response.
+ *
+ * All fields use explicit `T | null` (no optional `?:` per convention).
+ */
+export type AgentFrontmatter = {
+  /**
+   * Completion status signal from the agent.
+   * Null when omitted — engine treats it as "done" for backward compatibility.
+   */
+  status: FrontmatterStatus | null;
+
+  /**
+   * Suggested next role name for the moderator.
+   * The moderator is NOT obligated to follow this — it is advisory only.
+   * Null when the agent has no preference.
+   */
+  next: string | null;
+
+  /**
+   * Agent's self-assessed confidence in its output (0.0 – 1.0 inclusive).
+   * Null when omitted.
+   */
+  confidence: number | null;
+
+  /**
+   * Relative file paths or CAS hashes the agent considers its primary outputs.
+   * Used for GC ref-tracing and human-readable summaries.
+   * Empty array when omitted (never null — an absent list is an empty list).
+   */
+  artifacts: readonly string[];
+
+  /**
+   * Scope of the frontmatter signals.
+   * Defaults to "role" when omitted.
+   */
+  scope: FrontmatterScope;
+};
+
+// ── Parse output ─────────────────────────────────────────────────────────────
+
+/**
+ * Result of `parseFrontmatterMarkdown`: the structured frontmatter (if present)
+ * and the body (everything after the closing `---` fence, or the whole input
+ * if no frontmatter was found).
+ */
+export type ParsedFrontmatterMarkdown = {
+  /**
+   * Parsed frontmatter fields.  Null when no frontmatter block was detected
+   * (i.e. the document does not start with `---`).
+   */
+  frontmatter: AgentFrontmatter | null;
+
+  /** Markdown body with frontmatter block stripped. Leading newline removed. */
+  body: string;
+};
+
+// ── Validation error ─────────────────────────────────────────────────────────
+
+export type FrontmatterValidationError =
+  | { field: "status"; message: string }
+  | { field: "next"; message: string }
+  | { field: "confidence"; message: string }
+  | { field: "artifacts"; message: string }
+  | { field: "scope"; message: string };

packages/workflow-util/src/index.ts

@@ -1,6 +1,17 @@
 export { err, ok } from "@uncaged/workflow-protocol";
 export { encodeUint64AsCrockford } from "./base32.js";
 export { env } from "./env.js";
+export {
+  parseFrontmatterMarkdown,
+  validateFrontmatter,
+} from "./frontmatter-markdown/index.js";
+export type {
+  AgentFrontmatter,
+  FrontmatterScope,
+  FrontmatterStatus,
+  FrontmatterValidationError,
+  ParsedFrontmatterMarkdown,
+} from "./frontmatter-markdown/index.js";
 export { createLogger } from "./logger.js";
 export { normalizeRefsField } from "./refs-field.js";
 export { getDefaultWorkflowStorageRoot, getGlobalCasDir } from "./storage-root.js";