feat: add actor skill — frontmatter protocol + CAS reference

Adds 'uwf skill actor' command for agents executing workflow roles.
Covers the two things an actor needs to know:
1. Frontmatter output protocol (status field, schema-defined fields)
2. CAS operations (put, get, refs, walk, merkle DAG pattern)

Refs #540

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

@@ -0,0 +1,68 @@
+export function generateActorReference(): string {
+  return `# Actor Reference
+
+You are executing a workflow role. Your system prompt defines your goal, procedure, and output requirements. This reference covers two things you need to know about the workflow engine.
+
+## 1. Frontmatter Output Protocol
+
+Your response **MUST** begin with a YAML frontmatter block at byte position 0 — no preamble text before it.
+
+\`\`\`
+---
+status: done
+myField: some value
+---
+
+... markdown body (your work, explanation, notes) ...
+\`\`\`
+
+### Standard Field
+
+| Field | Values | Default | Description |
+|-------|--------|---------|-------------|
+| \`status\` | \`done\`, \`needs_input\`, \`in_progress\`, \`failed\` | \`done\` | Completion signal — determines which graph edge the moderator follows next |
+
+### Schema-Defined Fields
+
+Your role's output schema (shown in the system prompt under "Deliverable Format") defines additional fields. Output **only** the fields listed there — do not invent extra fields.
+
+### Body
+
+Everything after the closing \`---\` fence is the markdown body. Use it for explanations, logs, or human-readable notes. The body is stored but not parsed by the engine.
+
+### Retry
+
+If the engine cannot parse your frontmatter, it will ask you to retry (up to 2 times). Just output the corrected frontmatter block — don't panic.
+
+## 2. CAS (Content-Addressable Store)
+
+Your frontmatter output is automatically stored in CAS. You can also **use CAS directly** to store intermediate artifacts, build merkle DAGs for large outputs, or reference data from previous steps.
+
+### Commands
+
+\`\`\`
+uwf cas put-text <text>           # store plain text, print hash
+uwf cas put <type-hash> <json>    # store typed JSON data, print hash
+uwf cas get <hash>                # read a CAS node (type + payload)
+uwf cas has <hash>                # check if a hash exists
+uwf cas refs <hash>               # list direct references from a node
+uwf cas walk <hash>               # recursive traversal from a node
+uwf cas schema list               # list registered schemas
+uwf cas schema get <hash>         # show a schema definition
+\`\`\`
+
+### Merkle DAG Pattern
+
+For large outputs, store parts individually and reference their hashes:
+
+\`\`\`bash
+# Store individual sections
+HASH1=$(uwf cas put-text "section 1 content")
+HASH2=$(uwf cas put-text "section 2 content")
+
+# Reference hashes in your frontmatter or in a parent node
+\`\`\`
+
+This enables progressive loading — consumers can fetch the root and resolve children on demand.
+`;
+}

packages/workflow-util/src/index.ts

@@ -1,3 +1,4 @@
+export { generateActorReference } from "./actor-reference.js";
 export { generateArchitectureReference } from "./architecture-reference.js";
 export { encodeUint64AsCrockford } from "./base32.js";
 export { generateCliReference } from "./cli-reference.js";