feat(protocol): add edge prompt to Transition + EvaluateResult (#402)

- Transition type gains prompt: string | null
- evaluate() returns EvaluateResult { role, prompt } instead of string
- normalizeGraph coerces prompt: undefined → null
- spawnAgent passes edge prompt via UWF_EDGE_PROMPT env
- AgentContext gains edgePrompt field

Refs #402

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

@@ -133,6 +133,7 @@ export async function buildContext(threadId: ThreadId, role: string): Promise<Ag
   }
 
   const steps = await buildHistory(store, chain.stepsNewestFirst);
+  const edgePrompt = process.env.UWF_EDGE_PROMPT ?? null;
 
   return {
     threadId,
@@ -142,6 +143,7 @@ export async function buildContext(threadId: ThreadId, role: string): Promise<Ag
     workflow,
     store,
     outputFormatInstruction: "",
+    edgePrompt,
   };
 }
 
@@ -178,6 +180,7 @@ export async function buildContextWithMeta(
   }
 
   const steps = await buildHistory(store, chain.stepsNewestFirst);
+  const edgePrompt = process.env.UWF_EDGE_PROMPT ?? null;
 
   return {
     threadId,
@@ -187,6 +190,7 @@ export async function buildContextWithMeta(
     workflow,
     store,
     outputFormatInstruction: "",
+    edgePrompt,
     meta: { storageRoot, store, schemas, headHash, chain },
   };
 }

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

@@ -12,6 +12,12 @@ export type AgentContext = ModeratorContext & {
    * role's output schema.  Populated by `createAgent` at run time.
    */
   outputFormatInstruction: string;
+  /**
+   * Edge prompt from the graph transition that led to this role.
+   * null on first entry (use full role definition), non-null on re-entry
+   * (use as continuation instruction from moderator).
+   */
+  edgePrompt: string | null;
 };
 
 export type AgentRunResult = {