diff --git a/src/cli/services/__tests__/hookDispatchService.test.ts b/src/cli/services/__tests__/hookDispatchService.test.ts
index 4452583..8513209 100644
--- a/src/cli/services/__tests__/hookDispatchService.test.ts
+++ b/src/cli/services/__tests__/hookDispatchService.test.ts
@@ -589,7 +589,7 @@ describe('HookDispatchService session lifecycle', () => {
     expect(stopResult.output).toEqual({ continue: true });
   });
 
-  it('emits Stop workflow guidance when a PREVC workflow is active', async () => {
+  it('emits Codex Stop workflow guidance as a systemMessage when a PREVC workflow is active', async () => {
     const workflowService = await WorkflowService.create(tempDir);
     await workflowService.init({
       name: 'feature-x',
@@ -615,12 +615,11 @@ describe('HookDispatchService session lifecycle', () => {
 
     expect(stopResult.exitCode).toBe(0);
     expect(stopResult.output).toMatchObject({
-      hookSpecificOutput: {
-        hookEventName: 'Stop',
-        additionalContext: expect.stringContaining('feature-x'),
-      },
+      continue: true,
+      systemMessage: expect.stringContaining('feature-x'),
     });
     expect(stopResult.output).not.toHaveProperty('source');
+    expect(stopResult.output).not.toHaveProperty('hookSpecificOutput');
   });
 
   it.each(['Stop', 'SubagentStop'])(
diff --git a/src/integrations/__tests__/hookRoundTrip.test.ts b/src/integrations/__tests__/hookRoundTrip.test.ts
index 2620703..bb2f4b0 100644
--- a/src/integrations/__tests__/hookRoundTrip.test.ts
+++ b/src/integrations/__tests__/hookRoundTrip.test.ts
@@ -218,6 +218,26 @@ describe('hook mapper unit tests', () => {
       });
     });
 
+    it('emits Stop workflow guidance as a Codex systemMessage', () => {
+      const output = mapCodexResponse(codexStopFixture, {
+        ok: true,
+        tool: 'workflow-guide',
+        source: 'codex',
+        result: {
+          kind: 'json',
+          data: {
+            workflow: { active: true },
+            excerpt: 'dotcontext workflow guide:\nWorkflow "feature-x" - phase V.',
+          },
+        },
+      });
+
+      expect(output).toEqual({
+        continue: true,
+        systemMessage: expect.stringContaining('feature-x'),
+      });
+    });
+
     it('suppresses Stop guidance during reentry', () => {
       const output = mapCodexResponse(
         { ...codexStopFixture, sessionEndActive: true },
@@ -535,8 +555,9 @@ describe('hook round-trip integrations', () => {
       },
       (output: ReturnType<typeof mapCodexResponse>) => {
         expect(output).not.toHaveProperty('source');
-        expect(output.hookSpecificOutput?.hookEventName).toBe('Stop');
-        expect(output.hookSpecificOutput?.additionalContext).toContain('feature-x');
+        expect(output).not.toHaveProperty('hookSpecificOutput');
+        expect(output.continue).toBe(true);
+        expect(output.systemMessage).toContain('feature-x');
       },
     ],
   ])('%s envelope round-trips through adapter and response mapper', async (
diff --git a/src/integrations/codex/hooks/mapCodexResponse.ts b/src/integrations/codex/hooks/mapCodexResponse.ts
index 8208dbd..c777e72 100644
--- a/src/integrations/codex/hooks/mapCodexResponse.ts
+++ b/src/integrations/codex/hooks/mapCodexResponse.ts
@@ -10,6 +10,21 @@ import type { CodexHookInput } from './mapCodexEvent';
 
 export type CodexHookOutput = Omit<HostHookOutput, 'source'>;
 
+function mapCodexStopOutput(output: CodexHookOutput): CodexHookOutput {
+  const { hookSpecificOutput, ...rest } = output;
+  const additionalContext = hookSpecificOutput?.additionalContext;
+
+  if (!additionalContext) {
+    return output;
+  }
+
+  return {
+    ...rest,
+    continue: rest.continue ?? true,
+    systemMessage: rest.systemMessage ?? additionalContext,
+  };
+}
+
 export function mapCodexResponse(
   event: CodexHookInput,
   response: HarnessHookResponse
@@ -17,7 +32,13 @@ export function mapCodexResponse(
   const hookEventName =
     typeof event.hook_event_name === 'string' ? event.hook_event_name : 'unknown';
 
-  return mapHostHookResponseForSource('codex', hookEventName, response, {
+  const output = mapHostHookResponseForSource('codex', hookEventName, response, {
     suppressAdditionalContext: isSessionEndReentry(event),
   }) as CodexHookOutput;
+
+  if (hookEventName === 'Stop') {
+    return mapCodexStopOutput(output);
+  }
+
+  return output;
 }