feat(hooks): display hook system messages in UI (#24616)

packages/core/src/hooks/hookRunner.test.ts

@@ -204,7 +204,11 @@ describe('HookRunner', () => {
       };
 
       it('should execute command hook successfully', async () => {
-        const mockOutput = { decision: 'allow', reason: 'All good' };
+        const mockOutput = {
+          decision: 'allow',
+          reason: 'All good',
+          format: 'json',
+        };
 
         // Mock successful execution
         mockSpawn.mockStdoutOn.mockImplementation(
@@ -623,6 +627,7 @@ describe('HookRunner', () => {
         hookSpecificOutput: {
           additionalContext: 'Context from hook 1',
         },
+        format: 'json',
       };
 
       let hookCallCount = 0;
@@ -803,6 +808,7 @@ describe('HookRunner', () => {
       expect(result.success).toBe(true);
       expect(result.exitCode).toBe(0);
       // Should convert plain text to structured output
+      expect(result.outputFormat).toBe('text');
       expect(result.output).toEqual({
         decision: 'allow',
         systemMessage: invalidJson,
@@ -835,6 +841,7 @@ describe('HookRunner', () => {
       );
 
       expect(result.success).toBe(true);
+      expect(result.outputFormat).toBe('text');
       expect(result.output).toEqual({
         decision: 'allow',
         systemMessage: malformedJson,
@@ -868,6 +875,7 @@ describe('HookRunner', () => {
 
       expect(result.success).toBe(false);
       expect(result.exitCode).toBe(1);
+      expect(result.outputFormat).toBe('text');
       expect(result.output).toEqual({
         decision: 'allow',
         systemMessage: `Warning: ${invalidJson}`,
@@ -901,6 +909,7 @@ describe('HookRunner', () => {
 
       expect(result.success).toBe(false);
       expect(result.exitCode).toBe(2);
+      expect(result.outputFormat).toBe('text');
       expect(result.output).toEqual({
         decision: 'deny',
         reason: invalidJson,
@@ -936,7 +945,11 @@ describe('HookRunner', () => {
     });
 
     it('should handle double-encoded JSON string', async () => {
-      const mockOutput = { decision: 'allow', reason: 'All good' };
+      const mockOutput = {
+        decision: 'allow',
+        reason: 'All good',
+        format: 'json',
+      };
       const doubleEncodedJson = JSON.stringify(JSON.stringify(mockOutput));
 
       mockSpawn.mockStdoutOn.mockImplementation(