fix: StepOutput.sessionId → string | null, legacy fallback → null

Breaking changes:
- AgentRunResult now requires sessionId field
- AgentOptions now requires continue function
- Agent CLI outputs JSON {stepHash, sessionId} instead of plain CAS hash
- Engine parses JSON output (with legacy CAS hash fallback)

New features:
- Frontmatter validation retry: if agent output lacks valid frontmatter,
  engine calls agent.continue() up to 2 times with correction message
- Session tracking: sessionId flows from agent → engine → StepOutput
- Hermes agent: session parse failure is now a hard error (no raw text fallback)
- Hermes agent: supports --resume for continue sessions

Closes #384

.workflows/solve-issue.yaml

@@ -20,8 +20,8 @@ roles:
       2. Revise the test spec accordingly
 
       After producing the test spec:
-      1. Store it via `uwf cas put "<markdown content>"` and capture the returned hash
-      2. Put the hash in meta.plan (required when status=ready)
+      1. Store it via `uwf cas put-text "<markdown content>"` and capture the returned hash
+      2. Put the hash in frontmatter.plan (required when status=ready)
     output: "Output a brief summary of the test spec. Frontmatter must include: status (ready or insufficient_info) and plan (CAS hash of the test spec, required when status=ready)."
     frontmatter:
       type: object

packages/cli-workflow/src/cli.ts

@@ -7,6 +7,7 @@ import {
   cmdCasGet,
   cmdCasHas,
   cmdCasPut,
+  cmdCasPutText,
   cmdCasRefs,
   cmdCasReindex,
   cmdCasSchemaGet,
@@ -295,6 +296,17 @@ cas
     });
   });
 
+cas
+  .command("put-text")
+  .description("Store a plain text string, print its hash")
+  .argument("<text>", "Text content to store")
+  .action((text: string) => {
+    const storageRoot = resolveStorageRoot();
+    runAction(async () => {
+      writeOutput(await cmdCasPutText(storageRoot, text));
+    });
+  });
+
 cas
   .command("has")
   .description("Check if a hash exists")

packages/cli-workflow/src/commands/cas.ts

@@ -2,9 +2,11 @@ import { readFileSync } from "node:fs";
 import { join } from "node:path";
 
 import type { JSONSchema, Store } from "@uncaged/json-cas";
-import { bootstrap, getSchema, refs, walk } from "@uncaged/json-cas";
+import { bootstrap, getSchema, putSchema, refs, walk } from "@uncaged/json-cas";
 import { createFsStore } from "@uncaged/json-cas-fs";
 
+import { TEXT_SCHEMA } from "../schemas.js";
+
 // ---- Helpers ----
 
 function openStore(storageRoot: string): Store {
@@ -121,3 +123,10 @@ export async function cmdCasSchemaGet(storageRoot: string, hash: string): Promis
   }
   return schema;
 }
+
+export async function cmdCasPutText(storageRoot: string, text: string): Promise<{ hash: string }> {
+  const store = openStore(storageRoot);
+  const typeHash = await putSchema(store, TEXT_SCHEMA);
+  const hash = await store.put(typeHash, text);
+  return { hash };
+}

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

@@ -200,6 +200,7 @@ export async function cmdThreadShow(storageRoot: string, threadId: ThreadId): Pr
       thread: threadId,
       head: activeHead,
       done: false,
+      sessionId: null,
     };
   }
 
@@ -210,6 +211,7 @@ export async function cmdThreadShow(storageRoot: string, threadId: ThreadId): Pr
       thread: threadId,
       head: hist.head,
       done: true,
+      sessionId: null,
     };
   }
 
@@ -624,7 +626,12 @@ function resolveAgentConfig(
   return agentConfig;
 }
 
-function spawnAgent(agent: AgentConfig, threadId: ThreadId, role: string): CasRef {
+type SpawnAgentResult = {
+  stepHash: CasRef;
+  sessionId: string | null;
+};
+
+function spawnAgent(agent: AgentConfig, threadId: ThreadId, role: string): SpawnAgentResult {
   const argv = [...agent.args, threadId, role];
   let stdout: string;
   try {
@@ -646,10 +653,24 @@ function spawnAgent(agent: AgentConfig, threadId: ThreadId, role: string): CasRe
   }
 
   const line = stdout.trim().split("\n").pop()?.trim() ?? "";
-  if (!isCasRef(line)) {
-    fail(`agent stdout is not a valid CAS hash: ${line || "(empty)"}`);
+
+  // Try JSON output first (new protocol)
+  try {
+    const parsed = JSON.parse(line) as Record<string, unknown>;
+    const stepHash = parsed.stepHash;
+    const sessionId = parsed.sessionId;
+    if (typeof stepHash === "string" && isCasRef(stepHash) && typeof sessionId === "string") {
+      return { stepHash, sessionId };
+    }
+  } catch {
+    // Not JSON — fall through to legacy CAS hash parsing
   }
-  return line;
+
+  // Legacy: plain CAS hash on stdout
+  if (!isCasRef(line)) {
+    fail(`agent stdout is not a valid CAS hash or JSON: ${line || "(empty)"}`);
+  }
+  return { stepHash: line, sessionId: null };
 }
 
 async function archiveThread(
@@ -698,6 +719,7 @@ export async function cmdThreadStep(
       thread: threadId,
       head: headHash,
       done: true,
+      sessionId: null,
     };
   }
 
@@ -706,7 +728,7 @@ export async function cmdThreadStep(
   const agent = resolveAgentConfig(config, workflow, role, agentOverride);
 
   loadDotenv({ path: getEnvPath(storageRoot) });
-  const newHead = spawnAgent(agent, threadId, role);
+  const { stepHash: newHead, sessionId } = spawnAgent(agent, threadId, role);
 
   // Re-create store to pick up nodes written by the agent subprocess
   const uwfAfter = await createUwfStore(storageRoot);
@@ -737,6 +759,7 @@ export async function cmdThreadStep(
     thread: threadId,
     head: newHead,
     done,
+    sessionId,
   };
 }
 

packages/cli-workflow/src/schemas.ts

@@ -2,10 +2,13 @@ import type { Hash, Store } from "@uncaged/json-cas";
 import { putSchema } from "@uncaged/json-cas";
 import { START_NODE_SCHEMA, STEP_NODE_SCHEMA, WORKFLOW_SCHEMA } from "@uncaged/workflow-protocol";
 
+export const TEXT_SCHEMA = { type: "string" as const };
+
 export type UwfSchemaHashes = {
   workflow: Hash;
   startNode: Hash;
   stepNode: Hash;
+  text: Hash;
 };
 
 /**
@@ -13,10 +16,11 @@ export type UwfSchemaHashes = {
  * Idempotent: safe to call on every CLI invocation.
  */
 export async function registerUwfSchemas(store: Store): Promise<UwfSchemaHashes> {
-  const [workflow, startNode, stepNode] = await Promise.all([
+  const [workflow, startNode, stepNode, text] = await Promise.all([
     putSchema(store, WORKFLOW_SCHEMA),
     putSchema(store, START_NODE_SCHEMA),
     putSchema(store, STEP_NODE_SCHEMA),
+    putSchema(store, TEXT_SCHEMA),
   ]);
-  return { workflow, startNode, stepNode };
+  return { workflow, startNode, stepNode, text };
 }

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

@@ -1,4 +1,5 @@
 import { spawn } from "node:child_process";
+import type { Store } from "@uncaged/json-cas";
 
 import {
   type AgentContext,
@@ -10,7 +11,6 @@ import {
 import {
   loadHermesSession,
   parseSessionIdFromStdout,
-  storeHermesRawOutput,
   storeHermesSessionDetail,
 } from "./session-detail.js";
 
@@ -52,17 +52,8 @@ export function buildHermesPrompt(ctx: AgentContext): string {
   return parts.join("\n");
 }
 
-function spawnHermesChat(prompt: string): Promise<{ stdout: string; stderr: string }> {
+function spawnHermes(args: string[]): Promise<{ stdout: string; stderr: string }> {
   return new Promise((resolve, reject) => {
-    const args = [
-      "chat",
-      "-q",
-      prompt,
-      "--yolo",
-      "--max-turns",
-      String(HERMES_MAX_TURNS),
-      "--quiet",
-    ];
     const child = spawn(HERMES_COMMAND, args, {
       env: process.env,
       shell: false,
@@ -94,23 +85,73 @@ function spawnHermesChat(prompt: string): Promise<{ stdout: string; stderr: stri
   });
 }
 
+function spawnHermesChat(prompt: string): Promise<{ stdout: string; stderr: string }> {
+  return spawnHermes([
+    "chat",
+    "-q",
+    prompt,
+    "--yolo",
+    "--max-turns",
+    String(HERMES_MAX_TURNS),
+    "--quiet",
+  ]);
+}
+
+function spawnHermesResume(
+  sessionId: string,
+  message: string,
+): Promise<{ stdout: string; stderr: string }> {
+  return spawnHermes([
+    "chat",
+    "--resume",
+    sessionId,
+    "-q",
+    message,
+    "--yolo",
+    "--max-turns",
+    String(HERMES_MAX_TURNS),
+    "--quiet",
+  ]);
+}
+
+function parseSessionId(stdout: string, stderr: string): string {
+  const sessionId = parseSessionIdFromStdout(stderr) ?? parseSessionIdFromStdout(stdout);
+  if (sessionId === null) {
+    throw new Error(
+      "Failed to parse session_id from hermes output.\n" +
+        `stderr (first 200 chars): ${stderr.slice(0, 200)}\n` +
+        `stdout (first 200 chars): ${stdout.slice(0, 200)}`,
+    );
+  }
+  return sessionId;
+}
+
+async function buildResultFromSession(sessionId: string, store: Store): Promise<AgentRunResult> {
+  const session = await loadHermesSession(sessionId);
+  if (session === null) {
+    throw new Error(`Failed to load hermes session file for session_id: ${sessionId}`);
+  }
+  const { detailHash, output } = await storeHermesSessionDetail(store, session);
+  return { output, detailHash, sessionId };
+}
+
 async function runHermes(ctx: AgentContext): Promise<AgentRunResult> {
   const fullPrompt = buildHermesPrompt(ctx);
   const { stdout, stderr } = await spawnHermesChat(fullPrompt);
-  const { store } = ctx;
+  const sessionId = parseSessionId(stdout, stderr);
+  return buildResultFromSession(sessionId, ctx.store);
+}
 
-  // --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) {
-      const { detailHash, output } = await storeHermesSessionDetail(store, session);
-      return { output, detailHash };
-    }
-  }
-
-  const detailHash = await storeHermesRawOutput(store, stdout);
-  return { output: stdout, detailHash };
+async function continueHermes(
+  sessionId: string,
+  message: string,
+  store: Store,
+): Promise<AgentRunResult> {
+  const { stdout, stderr } = await spawnHermesResume(sessionId, message);
+  // Resume may return a new session_id
+  const newSessionId = parseSessionIdFromStdout(stderr) ?? parseSessionIdFromStdout(stdout);
+  const resolvedId = newSessionId ?? sessionId;
+  return buildResultFromSession(resolvedId, store);
 }
 
 /** Agent CLI factory: parses argv, runs Hermes, extracts output, writes StepNode. */
@@ -118,5 +159,6 @@ export function createHermesAgent(): () => Promise<void> {
   return createAgent({
     name: "hermes",
     run: runHermes,
+    continue: continueHermes,
   });
 }

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

@@ -12,4 +12,10 @@ 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";
+export type {
+  AgentContext,
+  AgentContinueFn,
+  AgentOptions,
+  AgentRunFn,
+  AgentRunResult,
+} from "./types.js";

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

@@ -3,11 +3,12 @@ import type { CasRef, StepNodePayload, ThreadId } from "@uncaged/workflow-protoc
 import { config as loadDotenv } from "dotenv";
 import { buildOutputFormatInstruction } from "./build-output-format-instruction.js";
 import { buildContextWithMeta } from "./context.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";
+import { getEnvPath, resolveStorageRoot } from "./storage.js";
+import type { AgentOptions } from "./types.js";
+
+const MAX_FRONTMATTER_RETRIES = 2;
 
 function fail(message: string): never {
   process.stderr.write(`${message}\n`);
@@ -66,31 +67,16 @@ async function writeStepNode(options: {
   return hash;
 }
 
-async function runAgent(options: AgentOptions, ctx: AgentContext): Promise<AgentRunResult> {
-  return runWithMessage("agent run failed", () => options.run(ctx));
-}
-
-async function extractOutput(
+async function tryExtractOutput(
   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);
-
+): Promise<CasRef | null> {
+  const fastPath = await tryFrontmatterFastPath(rawOutput, outputSchema, ctx.meta.store);
   if (fastPath !== null) {
     return fastPath.outputHash;
   }
-
-  const config = await runWithMessage("failed to load config", () =>
-    loadWorkflowConfig(storageRoot),
-  );
-  const extracted = await runWithMessage("extract failed", () =>
-    extract(rawOutput, outputSchema, config),
-  );
-  return extracted.hash;
+  return null;
 }
 
 async function persistStep(options: {
@@ -112,10 +98,18 @@ async function persistStep(options: {
   });
 }
 
+export type AgentCliOutput = {
+  stepHash: CasRef;
+  sessionId: string;
+};
+
 /**
  * Create an agent CLI entrypoint.
  * Parses argv (`<thread-id> <role>`), runs the agent, extracts structured output,
- * writes StepNode to CAS, and prints the new node hash to stdout.
+ * writes StepNode to CAS, and prints JSON result to stdout.
+ *
+ * If frontmatter extraction fails, retries up to MAX_FRONTMATTER_RETRIES times
+ * by calling agent.continue() with a correction message.
  */
 export function createAgent(options: AgentOptions): () => Promise<void> {
   return async function main(): Promise<void> {
@@ -135,13 +129,31 @@ export function createAgent(options: AgentOptions): () => Promise<void> {
       ctx.outputFormatInstruction = buildOutputFormatInstruction(frontmatterSchema);
     }
 
-    const agentResult = await runAgent(options, ctx);
-    const outputHash = await extractOutput(
-      agentResult.output,
-      roleDef.frontmatter,
-      storageRoot,
-      ctx,
-    );
+    let agentResult = await runWithMessage("agent run failed", () => options.run(ctx));
+
+    // Try to extract frontmatter; retry via continue if it fails
+    let outputHash = await tryExtractOutput(agentResult.output, roleDef.frontmatter, ctx);
+
+    for (let retry = 0; retry < MAX_FRONTMATTER_RETRIES && outputHash === null; retry++) {
+      const correctionMessage =
+        "Your previous response did not contain valid YAML frontmatter matching the role schema.\n" +
+        "You MUST begin your response with a YAML frontmatter block (--- delimited).\n" +
+        "Please output ONLY the corrected frontmatter block followed by your work.";
+
+      agentResult = await runWithMessage("agent continue failed", () =>
+        options.continue(agentResult.sessionId, correctionMessage, ctx.meta.store),
+      );
+      outputHash = await tryExtractOutput(agentResult.output, roleDef.frontmatter, ctx);
+    }
+
+    if (outputHash === null) {
+      fail(
+        "Agent output does not contain valid YAML frontmatter matching the role schema " +
+          `after ${MAX_FRONTMATTER_RETRIES} retries.\n` +
+          `Raw output (first 500 chars): ${agentResult.output.slice(0, 500)}`,
+      );
+    }
+
     const stepHash = await persistStep({
       ctx,
       outputHash,
@@ -149,6 +161,7 @@ export function createAgent(options: AgentOptions): () => Promise<void> {
       agentName: agentLabel(options.name),
     });
 
-    process.stdout.write(`${stepHash}\n`);
+    const result: AgentCliOutput = { stepHash, sessionId: agentResult.sessionId };
+    process.stdout.write(`${JSON.stringify(result)}\n`);
   };
 }

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

@@ -17,11 +17,19 @@ export type AgentContext = ModeratorContext & {
 export type AgentRunResult = {
   output: string;
   detailHash: string;
+  sessionId: string;
 };
 
+export type AgentContinueFn = (
+  sessionId: string,
+  message: string,
+  store: AgentContext["store"],
+) => Promise<AgentRunResult>;
+
 export type AgentRunFn = (ctx: AgentContext) => Promise<AgentRunResult>;
 
 export type AgentOptions = {
   name: string;
   run: AgentRunFn;
+  continue: AgentContinueFn;
 };

packages/workflow-protocol/src/types.ts

@@ -81,6 +81,7 @@ export type StepOutput = {
   thread: ThreadId;
   head: CasRef;
   done: boolean;
+  sessionId: string | null;
 };
 
 /** uwf thread steps — single step entry */

packages/workflow-util/src/cli-reference.ts

@@ -46,6 +46,8 @@ uwf cas get <hash>                # read a CAS node (type + payload)
             [--timestamp]         # include timestamp in output
 uwf cas put <type-hash> <data>    # store a node, print its hash
                                   # <data>: JSON file path or inline JSON string
+uwf cas put-text <text>           # store a plain text string, print its hash
+                                  # shortcut for put with the built-in text schema
 uwf cas has <hash>                # check if a hash exists
 uwf cas refs <hash>               # list direct CAS references from a node
 uwf cas walk <hash>               # recursive traversal from a node