feat(step-read): store assembled prompt in CAS, add --prompt flag

Store the fully assembled prompt sent to each agent in CAS as a text
node, referenced from StepNodePayload.assembledPrompt. This enables
exact reproduction of what the agent received for debugging hallucinations.

Changes:
- workflow-protocol: StepRecord + STEP_NODE_SCHEMA add assembledPrompt field
- workflow-util-agent: AgentRunResult includes assembledPrompt, run.ts stores it
- workflow-util-agent: schemas register TEXT_SCHEMA for prompt storage
- workflow-agent-claude-code: return assembled prompt from buildClaudeCodePrompt
- workflow-agent-hermes: return assembled prompt from buildHermesPrompt
- workflow-agent-builtin: return empty prompt (no prompt assembly)
- cli-workflow: step read --prompt renders the stored prompt
- All test fixtures updated for new field

Legacy steps without assembledPrompt show 'Prompt not recorded' message.

小橘 🍊

packages/workflow-protocol/src/__tests__/types.test.ts

@@ -25,6 +25,7 @@ describe("Protocol types for thread/edge location", () => {
         edgePrompt: "Plan the implementation",
         startedAtMs: Date.now(),
         completedAtMs: Date.now() + 1000,
+    assembledPrompt: null,
         cwd: "/home/user/project",
       };
 

packages/workflow-protocol/src/schemas.ts

@@ -88,6 +88,9 @@ export const STEP_NODE_SCHEMA: JSONSchema = {
     startedAtMs: { type: "integer" },
     completedAtMs: { type: "integer" },
     cwd: { type: "string" },
+    assembledPrompt: {
+      anyOf: [{ type: "string", format: "cas_ref" }, { type: "null" }],
+    },
   },
   additionalProperties: false,
 };

packages/workflow-protocol/src/types.ts

@@ -20,6 +20,8 @@ export type StepRecord = {
   completedAtMs: number;
   /** Working directory where the agent executed. Missing in legacy nodes → "". */
   cwd: string;
+  /** CAS ref to the fully assembled prompt sent to the agent. null for legacy steps. */
+  assembledPrompt: CasRef | null;
 };
 
 // ── 4.2 Workflow 定义 ───────────────────────────────────────────────