feat(12-01): create decompose output schema

- Add TaskBreakdown type with number, name, description, type, dependencies
- Create decomposeOutputSchema discriminated union (questions/decompose_complete/error)
- Create decomposeOutputJsonSchema for Claude CLI --json-schema flag
- Update module docstring to include decompose mode

src/agent/schema.ts

@@ -8,6 +8,7 @@
  * - execute: Standard task execution (done/questions/error)
  * - discuss: Gather context through questions, output decisions
  * - breakdown: Decompose initiative into phases
+ * - decompose: Decompose phase into individual tasks
  */
 
 import { z } from 'zod';
@@ -61,6 +62,30 @@ const phaseBreakdownSchema = z.object({
 
 export type PhaseBreakdown = z.infer<typeof phaseBreakdownSchema>;
 
+/**
+ * Task type enum - mirrors database task.type column.
+ */
+const taskTypeSchema = z.enum([
+  'auto',
+  'checkpoint:human-verify',
+  'checkpoint:decision',
+  'checkpoint:human-action',
+]);
+
+/**
+ * A task from decompose output.
+ * Prompt instructs: { "number": 1, "name": "...", "description": "...", "type": "auto", "dependencies": [0] }
+ */
+const taskBreakdownSchema = z.object({
+  number: z.number().int().positive(),
+  name: z.string().min(1),
+  description: z.string(),
+  type: taskTypeSchema.default('auto'),
+  dependencies: z.array(z.number().int()).optional().default([]),
+});
+
+export type TaskBreakdown = z.infer<typeof taskBreakdownSchema>;
+
 // =============================================================================
 // EXECUTE MODE SCHEMA (default)
 // =============================================================================
@@ -346,3 +371,105 @@ export const breakdownOutputJsonSchema = {
     },
   ],
 };
+
+// =============================================================================
+// DECOMPOSE MODE SCHEMA
+// =============================================================================
+
+/**
+ * Decompose mode output schema.
+ * Agent asks questions OR completes with tasks.
+ *
+ * Prompt tells agent:
+ * - Output "questions" status when needing clarification
+ * - Output "decompose_complete" status with tasks array when done
+ */
+export const decomposeOutputSchema = z.discriminatedUnion('status', [
+  // Agent needs clarification
+  z.object({
+    status: z.literal('questions'),
+    questions: z.array(questionItemSchema),
+  }),
+  // Agent has decomposed phase into tasks
+  z.object({
+    status: z.literal('decompose_complete'),
+    tasks: z.array(taskBreakdownSchema),
+  }),
+  // Unrecoverable error
+  z.object({
+    status: z.literal('unrecoverable_error'),
+    error: z.string(),
+  }),
+]);
+
+export type DecomposeOutput = z.infer<typeof decomposeOutputSchema>;
+
+/**
+ * JSON Schema for decompose mode (passed to Claude CLI --json-schema)
+ */
+export const decomposeOutputJsonSchema = {
+  type: 'object',
+  oneOf: [
+    {
+      properties: {
+        status: { const: 'questions' },
+        questions: {
+          type: 'array',
+          items: {
+            type: 'object',
+            properties: {
+              id: { type: 'string' },
+              question: { type: 'string' },
+              options: {
+                type: 'array',
+                items: {
+                  type: 'object',
+                  properties: {
+                    label: { type: 'string' },
+                    description: { type: 'string' },
+                  },
+                  required: ['label'],
+                },
+              },
+            },
+            required: ['id', 'question'],
+          },
+        },
+      },
+      required: ['status', 'questions'],
+    },
+    {
+      properties: {
+        status: { const: 'decompose_complete' },
+        tasks: {
+          type: 'array',
+          items: {
+            type: 'object',
+            properties: {
+              number: { type: 'integer', minimum: 1 },
+              name: { type: 'string', minLength: 1 },
+              description: { type: 'string' },
+              type: {
+                type: 'string',
+                enum: ['auto', 'checkpoint:human-verify', 'checkpoint:decision', 'checkpoint:human-action'],
+              },
+              dependencies: {
+                type: 'array',
+                items: { type: 'integer' },
+              },
+            },
+            required: ['number', 'name', 'description'],
+          },
+        },
+      },
+      required: ['status', 'tasks'],
+    },
+    {
+      properties: {
+        status: { const: 'unrecoverable_error' },
+        error: { type: 'string' },
+      },
+      required: ['status', 'error'],
+    },
+  ],
+};