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';

apps/server/trpc/routers/errand.ts

@@ -1,7 +1,7 @@
 /**
  * Errand Router
  *
- * All 9 errand procedures: create, list, get, diff, complete, merge, delete, sendMessage, abandon.
+ * All 10 errand procedures: create, list, get, diff, complete, merge, delete, sendMessage, abandon, requestChanges.
  * Errands are small isolated changes that spawn a dedicated agent in a git worktree.
  */
 
@@ -17,8 +17,9 @@ import {
   requireBranchManager,
 } from './_helpers.js';
 import { writeErrandManifest } from '../../agent/file-io.js';
-import { buildErrandPrompt } from '../../agent/prompts/index.js';
+import { buildErrandPrompt, buildErrandRevisionPrompt } from '../../agent/prompts/index.js';
 import { join } from 'node:path';
+import { existsSync, rmSync } from 'node:fs';
 import { SimpleGitWorktreeManager } from '../../git/manager.js';
 import { ensureProjectClone, getProjectCloneDir } from '../../git/project-clones.js';
 import type { TRPCContext } from '../context.js';
@@ -441,6 +442,96 @@ export function errandProcedures(publicProcedure: ProcedureBuilder) {
           const updated = await repo.update(input.id, { status: 'abandoned' });
           return updated;
         }),
+
+      // -----------------------------------------------------------------------
+      // errand.requestChanges
+      // -----------------------------------------------------------------------
+      requestChanges: publicProcedure
+        .input(z.object({
+          id: z.string().min(1),
+          feedback: z.string().min(1),
+        }))
+        .mutation(async ({ ctx, input }) => {
+          const repo = requireErrandRepository(ctx);
+          const errand = await repo.findById(input.id);
+          if (!errand) {
+            throw new TRPCError({ code: 'NOT_FOUND', message: 'Errand not found' });
+          }
+
+          if (errand.status !== 'pending_review' && errand.status !== 'conflict') {
+            throw new TRPCError({
+              code: 'BAD_REQUEST',
+              message: `Cannot request changes on an errand with status '${errand.status}'`,
+            });
+          }
+
+          if (!errand.projectId) {
+            throw new TRPCError({ code: 'NOT_FOUND', message: 'Errand has no project' });
+          }
+          const project = await requireProjectRepository(ctx).findById(errand.projectId);
+          if (!project) {
+            throw new TRPCError({ code: 'NOT_FOUND', message: 'Project not found' });
+          }
+
+          // Resolve clone path and verify worktree still exists
+          const clonePath = await resolveClonePath(project, ctx);
+          const worktreeManager = new SimpleGitWorktreeManager(clonePath);
+          let worktree;
+          try {
+            worktree = await worktreeManager.get(errand.id);
+          } catch {
+            throw new TRPCError({
+              code: 'BAD_REQUEST',
+              message: 'Worktree no longer exists — cannot request changes. Delete and re-create the errand.',
+            });
+          }
+          if (!worktree) {
+            throw new TRPCError({
+              code: 'BAD_REQUEST',
+              message: 'Worktree no longer exists — cannot request changes. Delete and re-create the errand.',
+            });
+          }
+
+          // Clean up stale signal.json to prevent false completion detection
+          const signalPath = join(worktree.path, '.cw', 'output', 'signal.json');
+          if (existsSync(signalPath)) {
+            rmSync(signalPath);
+          }
+
+          // Build revision prompt and spawn new agent in existing worktree
+          const prompt = buildErrandRevisionPrompt(errand.description, input.feedback);
+          const agentManager = requireAgentManager(ctx);
+          let agent;
+          try {
+            agent = await agentManager.spawn({
+              prompt,
+              mode: 'errand',
+              cwd: worktree.path,
+              provider: undefined,
+            });
+          } catch (err) {
+            throw new TRPCError({
+              code: 'INTERNAL_SERVER_ERROR',
+              message: err instanceof Error ? err.message : String(err),
+            });
+          }
+
+          // Update manifest files
+          await writeErrandManifest({
+            agentWorkdir: worktree.path,
+            errandId: errand.id,
+            description: errand.description,
+            branch: errand.branch,
+            projectName: project.name,
+            agentId: agent.id,
+            agentName: agent.name,
+          });
+
+          // Transition back to active with new agent
+          await repo.update(errand.id, { status: 'active', agentId: agent.id });
+
+          return { id: errand.id, agentId: agent.id };
+        }),
     }),
   };
 }

apps/web/src/components/ErrandDetailPanel.tsx

@@ -1,14 +1,17 @@
 import { useState, useEffect } from 'react';
 import { motion, AnimatePresence } from 'motion/react';
-import { X } from 'lucide-react';
+import { X, RefreshCw } from 'lucide-react';
 import { Button } from '@/components/ui/button';
 import { Input } from '@/components/ui/input';
 import { StatusBadge } from '@/components/StatusBadge';
 import { AgentOutputViewer } from '@/components/AgentOutputViewer';
+import { ErrandDiffView } from '@/components/ErrandDiffView';
 import { trpc } from '@/lib/trpc';
 import { formatRelativeTime } from '@/lib/utils';
 import { toast } from 'sonner';
 
+type ActiveTab = 'output' | 'changes';
+
 interface ErrandDetailPanelProps {
   errandId: string;
   onClose: () => void;
@@ -16,13 +19,15 @@ interface ErrandDetailPanelProps {
 
 export function ErrandDetailPanel({ errandId, onClose }: ErrandDetailPanelProps) {
   const [message, setMessage] = useState('');
+  const [activeTab, setActiveTab] = useState<ActiveTab>('output');
+  const [feedback, setFeedback] = useState('');
 
   const errandQuery = trpc.errand.get.useQuery({ id: errandId });
   const errand = errandQuery.data;
 
   const diffQuery = trpc.errand.diff.useQuery(
     { id: errandId },
-    { enabled: errand?.status !== 'active' },
+    { enabled: !!errand },
   );
 
   const utils = trpc.useUtils();
@@ -66,6 +71,16 @@ export function ErrandDetailPanel({ errandId, onClose }: ErrandDetailPanelProps)
     },
   });
 
+  const requestChangesMutation = trpc.errand.requestChanges.useMutation({
+    onSuccess: () => {
+      utils.errand.list.invalidate();
+      errandQuery.refetch();
+      setFeedback('');
+      setActiveTab('output');
+      toast.success('Agent re-spawned with your feedback');
+    },
+  });
+
   // Escape key closes
   useEffect(() => {
     function onKeyDown(e: KeyboardEvent) {
@@ -167,13 +182,62 @@ export function ErrandDetailPanel({ errandId, onClose }: ErrandDetailPanelProps)
               {/* View: Active */}
               {errand.status === 'active' && (
                 <>
+                  {/* Tabs */}
+                  <div className="flex items-center gap-0 border-b border-border px-5">
+                    <button
+                      className={`px-3 py-2 text-sm font-medium border-b-2 transition-colors ${
+                        activeTab === 'output'
+                          ? 'border-primary text-foreground'
+                          : 'border-transparent text-muted-foreground hover:text-foreground'
+                      }`}
+                      onClick={() => setActiveTab('output')}
+                    >
+                      Output
+                    </button>
+                    <button
+                      className={`px-3 py-2 text-sm font-medium border-b-2 transition-colors ${
+                        activeTab === 'changes'
+                          ? 'border-primary text-foreground'
+                          : 'border-transparent text-muted-foreground hover:text-foreground'
+                      }`}
+                      onClick={() => setActiveTab('changes')}
+                    >
+                      Changes
+                    </button>
+                  </div>
+
                   <div className="flex-1 overflow-y-auto">
-                    {errand.agentId && (
+                    {activeTab === 'output' ? (
+                      errand.agentId ? (
                         <AgentOutputViewer
                           agentId={errand.agentId}
                           agentName={errand.agentAlias ?? undefined}
                           status={undefined}
                         />
+                      ) : null
+                    ) : (
+                      <div className="px-5 py-4">
+                        <div className="flex items-center justify-between mb-3">
+                          <span className="text-xs text-muted-foreground">Committed changes</span>
+                          <button
+                            onClick={() => diffQuery.refetch()}
+                            className="flex items-center gap-1 text-xs text-muted-foreground hover:text-foreground transition-colors"
+                            title="Refresh diff"
+                          >
+                            <RefreshCw className={`h-3 w-3 ${diffQuery.isFetching ? 'animate-spin' : ''}`} />
+                            Refresh
+                          </button>
+                        </div>
+                        {diffQuery.isLoading ? (
+                          <p className="text-sm text-muted-foreground">Loading diff…</p>
+                        ) : diffQuery.data?.diff ? (
+                          <ErrandDiffView diff={diffQuery.data.diff} />
+                        ) : (
+                          <p className="text-sm text-muted-foreground">
+                            No changes yet.
+                          </p>
+                        )}
+                      </div>
                     )}
                   </div>
 
@@ -258,9 +322,7 @@ export function ErrandDetailPanel({ errandId, onClose }: ErrandDetailPanelProps)
                       {diffQuery.isLoading ? (
                         <p className="text-sm text-muted-foreground">Loading diff…</p>
                       ) : diffQuery.data?.diff ? (
-                        <pre className="overflow-x-auto rounded border border-border bg-muted/50 p-4 text-xs font-mono whitespace-pre">
-                          {diffQuery.data.diff}
-                        </pre>
+                        <ErrandDiffView diff={diffQuery.data.diff} />
                       ) : (
                         <p className="text-sm text-muted-foreground">
                           No changes — branch has no commits.
@@ -269,6 +331,27 @@ export function ErrandDetailPanel({ errandId, onClose }: ErrandDetailPanelProps)
                     </div>
                   </div>
 
+                  {/* Request changes input */}
+                  <div className="border-t border-border px-5 py-3">
+                    <textarea
+                      value={feedback}
+                      onChange={(e) => setFeedback(e.target.value)}
+                      placeholder="Describe what needs to change…"
+                      className="w-full rounded-md border border-border bg-background px-3 py-2 text-sm placeholder:text-muted-foreground focus:outline-none focus:ring-1 focus:ring-ring resize-none"
+                      rows={2}
+                    />
+                    <div className="flex justify-end mt-2">
+                      <Button
+                        size="sm"
+                        variant="outline"
+                        disabled={!feedback.trim() || requestChangesMutation.isPending}
+                        onClick={() => requestChangesMutation.mutate({ id: errandId, feedback })}
+                      >
+                        {requestChangesMutation.isPending ? 'Sending…' : 'Request Changes'}
+                      </Button>
+                    </div>
+                  </div>
+
                   {/* Footer */}
                   <div className="flex items-center justify-between border-t border-border px-5 py-3">
                     <div className="flex gap-2">
@@ -338,9 +421,7 @@ export function ErrandDetailPanel({ errandId, onClose }: ErrandDetailPanelProps)
                     {/* Read-only diff */}
                     <div className="flex-1 overflow-y-auto px-5 py-4">
                       {diffQuery.data?.diff ? (
-                        <pre className="overflow-x-auto rounded border border-border bg-muted/50 p-4 text-xs font-mono whitespace-pre">
-                          {diffQuery.data.diff}
-                        </pre>
+                        <ErrandDiffView diff={diffQuery.data.diff} />
                       ) : (
                         <p className="text-sm text-muted-foreground">
                           No changes — branch has no commits.

apps/web/src/components/ErrandDiffView.tsx

@@ -0,0 +1,68 @@
+import { useMemo } from 'react';
+import { Plus, Minus } from 'lucide-react';
+import { parseUnifiedDiff } from '@/components/review/parse-diff';
+import { FileCard } from '@/components/review/FileCard';
+import type { ReviewComment, DiffLine } from '@/components/review/types';
+
+const emptyComments = new Map<string, ReviewComment[]>();
+const noop = () => {};
+
+interface ErrandDiffViewProps {
+  diff: string;
+}
+
+export function ErrandDiffView({ diff }: ErrandDiffViewProps) {
+  const files = useMemo(() => parseUnifiedDiff(diff), [diff]);
+
+  const totals = useMemo(() => {
+    let additions = 0;
+    let deletions = 0;
+    for (const f of files) {
+      additions += f.additions;
+      deletions += f.deletions;
+    }
+    return { additions, deletions };
+  }, [files]);
+
+  if (files.length === 0) {
+    return (
+      <p className="text-sm text-muted-foreground">No changes — branch has no commits.</p>
+    );
+  }
+
+  return (
+    <div className="space-y-3">
+      {/* Summary */}
+      <div className="flex items-center gap-3 text-xs text-muted-foreground">
+        <span>{files.length} file{files.length !== 1 ? 's' : ''} changed</span>
+        {totals.additions > 0 && (
+          <span className="flex items-center gap-0.5 text-diff-add-fg">
+            <Plus className="h-3 w-3" />
+            {totals.additions}
+          </span>
+        )}
+        {totals.deletions > 0 && (
+          <span className="flex items-center gap-0.5 text-diff-remove-fg">
+            <Minus className="h-3 w-3" />
+            {totals.deletions}
+          </span>
+        )}
+      </div>
+
+      {/* File cards */}
+      {files.map((file) => (
+        <FileCard
+          key={file.newPath}
+          file={file}
+          detail={file}
+          phaseId=""
+          commitMode={true}
+          commentsByLine={emptyComments}
+          onAddComment={noop as (filePath: string, lineNumber: number, lineType: DiffLine['type'], body: string) => void}
+          onResolveComment={noop}
+          onUnresolveComment={noop}
+        />
+      ))}
+    </div>
+  );
+}