refactor: Wire buildExecutePrompt into dispatch manager

Dispatch manager now wraps task descriptions with buildExecutePrompt()
so agents receive the full execution protocol. Update test to match
prompt wrapping. Add worktree isolation note to workspace layout.

src/agent/prompts/workspace.ts

@@ -16,7 +16,7 @@ export function buildWorkspaceLayout(agentCwd: string): string {
   }
 
   if (entries.length === 0) {
-    return `\n\n## Workspace Layout\n\nYour working directory is: ${agentCwd}`;
+    return `\n\n## Workspace Layout\n\nYour working directory is: ${agentCwd}\nThis is an isolated git worktree. Other agents may be working in parallel on separate branches — do not assume you have exclusive access to the repository.`;
   }
 
   const lines = entries.map(
@@ -26,6 +26,7 @@ export function buildWorkspaceLayout(agentCwd: string): string {
   return `\n\n## Workspace Layout
 
 Your working directory is: ${agentCwd}
+This is an isolated git worktree. Other agents may be working in parallel on separate branches — do not assume you have exclusive access to the repository.
 The following project directories contain the source code (git worktrees):
 
 ${lines.join('\n')}`;

src/dispatch/manager.test.ts

@@ -397,11 +397,11 @@ describe('DefaultDispatchManager', () => {
       const updatedTask = await taskRepository.findById(task.id);
       expect(updatedTask!.status).toBe('in_progress');
 
-      // Check spawn was called with correct params
+      // Check spawn was called with correct params (prompt is wrapped by buildExecutePrompt)
       expect(agentManager.spawn).toHaveBeenCalledWith(
         expect.objectContaining({
           taskId: task.id,
-          prompt: 'Do the thing',
+          prompt: expect.stringContaining('Do the thing'),
         })
       );
     });

src/dispatch/manager.ts

@@ -23,6 +23,7 @@ import type { PhaseRepository } from '../db/repositories/phase-repository.js';
 import type { Task } from '../db/schema.js';
 import type { DispatchManager, QueuedTask, DispatchResult } from './types.js';
 import { phaseBranchName, taskBranchName, isPlanningCategory, generateInitiativeBranch } from '../git/branch-naming.js';
+import { buildExecutePrompt } from '../agent/prompts/index.js';
 import { createModuleLogger } from '../logger/index.js';
 
 const log = createModuleLogger('dispatch');
@@ -371,7 +372,7 @@ export class DefaultDispatchManager implements DispatchManager {
       taskId: nextTask.taskId,
       initiativeId: task.initiativeId ?? undefined,
       phaseId: task.phaseId ?? undefined,
-      prompt: task.description || task.name,
+      prompt: buildExecutePrompt(task.description || task.name),
       baseBranch,
       branchName,
     });