feat: errand review & request changes

Add errand.requestChanges procedure that re-spawns an agent in the
existing worktree with user feedback. Replace raw <pre> diff blocks
with syntax-highlighted ErrandDiffView using FileCard components.
Add Output/Changes tabs to the active errand view.

apps/server/agent/prompts/errand.ts

@@ -14,3 +14,24 @@ If you cannot complete the change:
 
 Do not create any other output files.`;
 }
+
+export function buildErrandRevisionPrompt(description: string, feedback: string): string {
+  return `You are revising a previous change in an isolated worktree. The worktree already contains your prior work.
+
+Original description: ${description}
+
+The user reviewed your changes and requested revisions:
+
+${feedback}
+
+Make only the changes needed to address the feedback. Do not undo prior work unless the feedback specifically asks for it.
+When you are done, write .cw/output/signal.json:
+
+{ "status": "done", "result": { "message": "<one-sentence summary of what you changed>" } }
+
+If you cannot complete the change:
+
+{ "status": "error", "error": "<explanation>" }
+
+Do not create any other output files.`;
+}

apps/server/agent/prompts/index.ts

@@ -13,7 +13,7 @@ export { buildDetailPrompt } from './detail.js';
 export { buildRefinePrompt } from './refine.js';
 export { buildChatPrompt } from './chat.js';
 export type { ChatHistoryEntry } from './chat.js';
-export { buildErrandPrompt } from './errand.js';
+export { buildErrandPrompt, buildErrandRevisionPrompt } from './errand.js';
 export { buildWorkspaceLayout } from './workspace.js';
 export { buildPreviewInstructions } from './preview.js';
 export { buildConflictResolutionPrompt, buildConflictResolutionDescription } from './conflict-resolution.js';