Use plain dispatch for no-diff Forge validation

packages/forge/src/generated/stages.ts

@@ -169,7 +169,8 @@ export async function runForgeEngineAttempt(opts: {engineId:string,prompt:string
   // Forge is a code-changing workflow. API-only engines must run through
   // the tool-using agent loop; plain API chat can only return text and will
   // never modify the worktree.
-  const useAgent = !!opts.adapter.dispatchAgent && (!!engine.agent || !!engine.api);
+  const shouldUseAgentLoop = forgeMode === 'implement' || forgeMode === 'improve' || requireDiff;
+  const useAgent = shouldUseAgentLoop && !!opts.adapter.dispatchAgent && (!!engine.agent || !!engine.api);
   const onSpawn = (pid: number) => emitForgeEvent(opts.onEvent, 'engine:pid', opts.engineId, { engineId: opts.engineId, pid, phase: opts.metricPhase });
   try {
     if (useAgent) {
@@ -298,7 +299,7 @@ export async function runForgeEngineAttempt(opts: {engineId:string,prompt:string
   return { result, metric, dispatchResult, worktreePath: wtPath };
 }
 
-// @kern-source: stages:276
+// @kern-source: stages:277
 export async function runBaseline(opts: {cwd:string, baseSha:string, fitnessCmd:string, fitnessTimeout:number, forgeDir:string, onEvent?:ForgeEventCallback}): Promise<boolean> {
   opts.onEvent?.({ type: 'baseline:start' });
 
@@ -322,7 +323,7 @@ export async function runBaseline(opts: {cwd:string, baseSha:string, fitnessCmd:
   }
 }
 
-// @kern-source: stages:300
+// @kern-source: stages:301
 export async function runStage1(opts: {starter:string, forgePrompt:string, fitnessCmd:string, config:Required<AgonConfig>, registry:EngineRegistry, adapter:EngineAdapter, cwd:string, baseSha:string, forgeDir:string, worktrees:WorktreeEntry[], onEvent?:ForgeEventCallback, signal?:AbortSignal, taskClass?:string, enginePrompts?:Map<string,string>, forgeMode?:'implement'|'improve'|'validate', requireDiff?:boolean, baselinePasses?:boolean, acceptReviewOutput?:boolean}): Promise<StageResult> {
   opts.onEvent?.({ type: 'stage1:start', engineId: opts.starter });
   const root = repoRoot(opts.cwd);
@@ -352,7 +353,7 @@ export async function runStage1(opts: {starter:string, forgePrompt:string, fitne
   return { engineResults, accepted, winner: result?.pass ? result.engineId : null, metrics };
 }
 
-// @kern-source: stages:330
+// @kern-source: stages:331
 export async function runStage2(opts: {challengers:string[], forgePrompt:string, enginePrompts?:Map<string,string>, fitnessCmd:string, config:Required<AgonConfig>, registry:EngineRegistry, adapter:EngineAdapter, cwd:string, baseSha:string, forgeDir:string, existingResults:Map<string,EngineResult>, worktrees:WorktreeEntry[], onEvent?:ForgeEventCallback, signal?:AbortSignal, onResult?:(engineId:string,result:EngineResult,metric:DispatchMetric)=>'continue'|'finalize'|void, abortControllers?: Map<string,AbortController>, forgeMode?: 'implement'|'improve'|'validate', requireDiff?: boolean, baselinePasses?: boolean, acceptReviewOutput?: boolean, earlyFinalizeCount?: number}): Promise<StageResult> {
   opts.onEvent?.({ type: 'stage2:start' });
 
@@ -551,7 +552,7 @@ export async function runStage2(opts: {challengers:string[], forgePrompt:string,
   return { engineResults: allResults, accepted: false, winner: null, metrics };
 }
 
-// @kern-source: stages:529
+// @kern-source: stages:530
 export async function runStage2WithPeek(opts: {challengers:string[], forgePrompt:string, enginePrompts?:Map<string,string>, fitnessCmd:string, config:Required<AgonConfig>, registry:EngineRegistry, adapter:EngineAdapter, cwd:string, baseSha:string, forgeDir:string, existingResults:Map<string,EngineResult>, worktrees:WorktreeEntry[], onEvent?:ForgeEventCallback, signal?:AbortSignal, forgeMode?:'implement'|'improve'|'validate', requireDiff?:boolean, baselinePasses?:boolean, acceptReviewOutput?:boolean}): Promise<StageResult> {
   if (opts.challengers.length <= 1) {
     // Only one challenger — no peek possible, use normal stage2

packages/forge/src/kern/stages.kern

@@ -144,7 +144,8 @@ fn name=runForgeEngineAttempt async=true params="opts:{engineId:string,prompt:st
     // Forge is a code-changing workflow. API-only engines must run through
     // the tool-using agent loop; plain API chat can only return text and will
     // never modify the worktree.
-    const useAgent = !!opts.adapter.dispatchAgent && (!!engine.agent || !!engine.api);
+    const shouldUseAgentLoop = forgeMode === 'implement' || forgeMode === 'improve' || requireDiff;
+    const useAgent = shouldUseAgentLoop && !!opts.adapter.dispatchAgent && (!!engine.agent || !!engine.api);
     const onSpawn = (pid: number) => emitForgeEvent(opts.onEvent, 'engine:pid', opts.engineId, { engineId: opts.engineId, pid, phase: opts.metricPhase });
     try {
       if (useAgent) {

tests/unit/forge-finalize.test.ts

@@ -62,6 +62,110 @@ function makeRegistry(): EngineRegistry {
   return registry;
 }
 
+describe('forge validate dispatch routing', () => {
+  it('uses plain dispatch, not agent tools, for validate mode without required diff', async () => {
+    process.env.AGON_FINALIZE_TEST_KEY = 'test';
+    const repoDir = makeRepo();
+    const forgeDir = join(tmpdir(), `agon-forge-validate-route-${Date.now()}-${Math.random().toString(36).slice(2)}`);
+    tempDirs.push(forgeDir);
+    mkdirSync(forgeDir, { recursive: true });
+
+    const registry = new EngineRegistry();
+    registry.register({
+      id: 'api-agent',
+      displayName: 'api-agent',
+      api: { apiKeyEnv: 'AGON_FINALIZE_TEST_KEY' },
+      agent: { args: [] },
+      exec: { args: [] },
+      review: { args: [] },
+      timeout: 120,
+      tier: 'user',
+      schemaVersion: 3,
+      isLocal: false,
+    } as any);
+
+    const dispatch = vi.fn(async () => ({
+      exitCode: 0,
+      stdout: 'VALIDATE_ROUTE_OK '.repeat(8),
+      stderr: '',
+      timedOut: false,
+    }));
+    const dispatchAgent = vi.fn(async () => {
+      throw new Error('dispatchAgent should not run for validate/no-diff');
+    });
+
+    const manifest = await runForge(
+      {
+        task: 'validate without editing',
+        fitnessCmd: 'true',
+        cwd: repoDir,
+        forgeDir,
+        engines: ['api-agent'],
+        mode: 'validate',
+        requireDiff: false,
+        acceptReviewOutput: true,
+        baselineMayPass: true,
+        healthCheckEnabled: false,
+      } as any,
+      registry,
+      { isAvailable: async () => true, getVersion: async () => 'test', dispatch, dispatchAgent } as any,
+    );
+
+    expect(dispatch).toHaveBeenCalledTimes(1);
+    expect(dispatchAgent).not.toHaveBeenCalled();
+    expect(manifest.results['api-agent']).toMatchObject({ pass: true, status: 'no_diff_but_report' });
+  });
+
+  it('still uses agent tools for validate mode when a diff is required', async () => {
+    process.env.AGON_FINALIZE_TEST_KEY = 'test';
+    const repoDir = makeRepo();
+    const forgeDir = join(tmpdir(), `agon-forge-validate-agent-${Date.now()}-${Math.random().toString(36).slice(2)}`);
+    tempDirs.push(forgeDir);
+    mkdirSync(forgeDir, { recursive: true });
+
+    const registry = new EngineRegistry();
+    registry.register({
+      id: 'api-agent',
+      displayName: 'api-agent',
+      api: { apiKeyEnv: 'AGON_FINALIZE_TEST_KEY' },
+      agent: { args: [] },
+      exec: { args: [] },
+      review: { args: [] },
+      timeout: 120,
+      tier: 'user',
+      schemaVersion: 3,
+      isLocal: false,
+    } as any);
+
+    const dispatch = vi.fn(async () => ({ exitCode: 0, stdout: 'plain', stderr: '', timedOut: false }));
+    const dispatchAgent = vi.fn(async ({ cwd }: any) => {
+      writeFileSync(join(cwd, 'agent-change.txt'), 'changed by agent\n');
+      return { exitCode: 0, stdout: 'agent changed files', stderr: '', timedOut: false };
+    });
+
+    const manifest = await runForge(
+      {
+        task: 'validate but require a diff',
+        fitnessCmd: 'test -f agent-change.txt',
+        cwd: repoDir,
+        forgeDir,
+        engines: ['api-agent'],
+        mode: 'validate',
+        requireDiff: true,
+        acceptReviewOutput: true,
+        baselineMayPass: true,
+        healthCheckEnabled: false,
+      } as any,
+      registry,
+      { isAvailable: async () => true, getVersion: async () => 'test', dispatch, dispatchAgent } as any,
+    );
+
+    expect(dispatchAgent).toHaveBeenCalledTimes(1);
+    expect(dispatch).not.toHaveBeenCalled();
+    expect(manifest.results['api-agent']).toMatchObject({ pass: true });
+  });
+});
+
 describe('caller-driven forge finalize', () => {
   it('aborts in-flight stage2 engines when onResult requests finalize', async () => {
     process.env.AGON_FINALIZE_TEST_KEY = 'test';