feat(FN-4400): complete Step 3 — add heartbeat prompt template resolver

Fusion-Task-Id: FN-4400
Fusion-Task-Lineage: 0d4f9c48-5b8b-49eb-9cf3-d1d585ffe7fc

packages/engine/src/__tests__/heartbeat-procedure-resolver.test.ts

@@ -1,9 +1,18 @@
 import type { Agent, ProjectSettings } from "@fusion/core";
 import { describe, expect, it } from "vitest";
-import { resolveHeartbeatScopeDisciplineMode, selectHeartbeatProcedure } from "../heartbeat-procedure-resolver.js";
+import {
+  resolveHeartbeatPromptTemplate,
+  resolveHeartbeatScopeDisciplineMode,
+  selectHeartbeatProcedure,
+} from "../heartbeat-procedure-resolver.js";
 
 const project = (mode?: ProjectSettings["heartbeatScopeDiscipline"]) => ({ heartbeatScopeDiscipline: mode });
 const agent = (mode?: unknown) => ({ runtimeConfig: mode === undefined ? {} : { heartbeatScopeDiscipline: mode } }) as Pick<Agent, "runtimeConfig">;
+const projectTemplate = (template?: ProjectSettings["heartbeatPromptTemplate"]) => ({ heartbeatPromptTemplate: template });
+const templateAgent = (role: Agent["role"], template?: unknown) => ({
+  role,
+  runtimeConfig: template === undefined ? {} : { heartbeatPromptTemplate: template },
+}) as Pick<Agent, "runtimeConfig" | "role">;
 
 describe("resolveHeartbeatScopeDisciplineMode", () => {
   it.each(["strict", "lite", "off"] as const)("prefers agent override: %s", (mode) => {
@@ -31,6 +40,39 @@ describe("resolveHeartbeatScopeDisciplineMode", () => {
   });
 });
 
+describe("resolveHeartbeatPromptTemplate", () => {
+  it("prefers agent override over project and role defaults", () => {
+    expect(resolveHeartbeatPromptTemplate(projectTemplate("default"), templateAgent("triage", "compact"))).toBe("compact");
+  });
+
+  it("uses project setting when agent override is unset", () => {
+    expect(resolveHeartbeatPromptTemplate(projectTemplate("compact"), templateAgent("executor"))).toBe("compact");
+  });
+
+  it.each(["triage", "reviewer", "merger", "scheduler", "engineer", "custom"] as const)(
+    "defaults non-executor role %s to compact",
+    (role) => {
+      expect(resolveHeartbeatPromptTemplate(undefined, templateAgent(role))).toBe("compact");
+    },
+  );
+
+  it("defaults executor role to default", () => {
+    expect(resolveHeartbeatPromptTemplate(undefined, templateAgent("executor"))).toBe("default");
+  });
+
+  it("falls through invalid agent template to project", () => {
+    expect(resolveHeartbeatPromptTemplate(projectTemplate("compact"), templateAgent("executor", "invalid"))).toBe("compact");
+  });
+
+  it("falls through invalid project template to role default", () => {
+    expect(resolveHeartbeatPromptTemplate(projectTemplate("tiny" as never), templateAgent("triage"))).toBe("compact");
+  });
+
+  it("returns default when agent is undefined", () => {
+    expect(resolveHeartbeatPromptTemplate(projectTemplate("tiny" as never), undefined)).toBe("default");
+  });
+});
+
 describe("selectHeartbeatProcedure", () => {
   const procedures = {
     task: { strict: "task-strict", lite: "task-lite", off: "task-off" },

packages/engine/src/heartbeat-procedure-resolver.ts

@@ -1,11 +1,16 @@
-import type { Agent, HeartbeatScopeDisciplineMode, ProjectSettings } from "@fusion/core";
+import type { Agent, HeartbeatPromptTemplate, HeartbeatScopeDisciplineMode, ProjectSettings } from "@fusion/core";
 
 const VALID_MODES: readonly HeartbeatScopeDisciplineMode[] = ["strict", "lite", "off"] as const;
+const VALID_TEMPLATES: readonly HeartbeatPromptTemplate[] = ["default", "compact"] as const;
 
 function isHeartbeatScopeDisciplineMode(value: unknown): value is HeartbeatScopeDisciplineMode {
   return typeof value === "string" && (VALID_MODES as readonly string[]).includes(value);
 }
 
+function isHeartbeatPromptTemplate(value: unknown): value is HeartbeatPromptTemplate {
+  return typeof value === "string" && (VALID_TEMPLATES as readonly string[]).includes(value);
+}
+
 export function resolveHeartbeatScopeDisciplineMode(
   projectSettings: Pick<ProjectSettings, "heartbeatScopeDiscipline"> | undefined,
   agent: Pick<Agent, "runtimeConfig"> | undefined,
@@ -24,6 +29,28 @@ export function resolveHeartbeatScopeDisciplineMode(
   return "strict";
 }
 
+export function resolveHeartbeatPromptTemplate(
+  projectSettings: Pick<ProjectSettings, "heartbeatPromptTemplate"> | undefined,
+  agent: Pick<Agent, "runtimeConfig" | "role"> | undefined,
+): HeartbeatPromptTemplate {
+  const runtimeConfig = agent?.runtimeConfig as Record<string, unknown> | undefined;
+  const agentTemplate = runtimeConfig?.heartbeatPromptTemplate;
+  if (isHeartbeatPromptTemplate(agentTemplate)) {
+    return agentTemplate;
+  }
+
+  const projectTemplate = projectSettings?.heartbeatPromptTemplate;
+  if (isHeartbeatPromptTemplate(projectTemplate)) {
+    return projectTemplate;
+  }
+
+  if (!agent) {
+    return "default";
+  }
+
+  return agent.role === "executor" ? "default" : "compact";
+}
+
 export function selectHeartbeatProcedure<T>(
   mode: HeartbeatScopeDisciplineMode,
   isNoTaskRun: boolean,