feat: write/edit robustness — fuzzy patch applier + worktree checkpoints (v2.7.1)

#3 Fuzzy patch applier: new pure fuzzy-match.ts (locateMatch, exact→trim→
unicode-canon→Levenshtein≥0.66, refuse-on-ambiguous) wired into pending_changes
applyOne/rewindOne so local-model whitespace/unicode drift in old_string no
longer loses the edit.

#4 Worktree checkpoint + conversation-trim: checkpoints table + checkpoints.ts
(shadow-commit of tracked+untracked into refs/boocode/checkpoints, hooked into
the 3 external-agent dispatcher paths) + POST restore route (reset --hard +
clean -fd -> transcript trim -> backend-session reset) + "Restore to here" UI.

Built by 3 parallel agents; DB-integration testing caught a created_at
self-deletion bug. Coder suite 234 passing; server+coder build + web tsc clean.
Builds on v2.7.0-mit. openspec write-edit-robustness.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/web/src/components/MessageBubble.tsx

@@ -1,6 +1,6 @@
 import { useEffect, useState } from 'react';
 import type { ReactNode } from 'react';
-import { ChevronDown, ChevronRight, Copy, RefreshCw, Check, Share2, RotateCw, GitFork, Trash2, Brain } from 'lucide-react';
+import { ChevronDown, ChevronRight, Copy, RefreshCw, Check, Share2, RotateCw, GitFork, Trash2, Brain, History } from 'lucide-react';
 import { toast } from 'sonner';
 import type { Chat, ErrorReason, Message } from '@/api/types';
 import { api } from '@/api/client';
@@ -110,6 +110,10 @@ export interface MessageActions {
   onResend?: (chatId: string, content: string) => Promise<void>;
   onFork?: (chatId: string, messageId: string) => Promise<void>;
   onDelete?: (chatId: string, messageId: string) => Promise<void>;
+  // write-edit-robustness #4 (BooCoder only): reset the worktree to this
+  // message's pre-turn checkpoint and trim the transcript past it. BooChat
+  // passes no such callback → the "Restore to here" control never renders.
+  onRestoreCheckpoint?: (chatId: string, messageId: string) => Promise<void>;
 }
 
 interface Props {
@@ -119,6 +123,17 @@ interface Props {
   actions?: MessageActions;
   /** Hide actions that don't apply (fork, delete). */
   hideActions?: ('fork' | 'delete')[];
+  /**
+   * write-edit-robustness #4: this assistant message has a worktree checkpoint
+   * → render "Restore to here" (only when `actions.onRestoreCheckpoint` is also
+   * provided). CoderMessageList sets this from the checkpoint set.
+   */
+  hasCheckpoint?: boolean;
+  /**
+   * write-edit-robustness #4: suppress the restore control during an active
+   * turn (mirrors composer gating). Defaults to enabled.
+   */
+  restoreDisabled?: boolean;
 }
 
 function StatsLine({ message }: { message: Message }) {
@@ -155,16 +170,22 @@ function ActionRow({
   message,
   actions,
   hiddenSet,
+  hasCheckpoint = false,
+  restoreDisabled = false,
 }: {
   message: Message;
   actions?: MessageActions;
   hiddenSet: Set<string>;
+  hasCheckpoint?: boolean;
+  restoreDisabled?: boolean;
 }) {
   const [justCopied, setJustCopied] = useState(false);
   const [regenerating, setRegenerating] = useState(false);
   const [forking, setForking] = useState(false);
   const [deleteOpen, setDeleteOpen] = useState(false);
   const [deleting, setDeleting] = useState(false);
+  const [restoreOpen, setRestoreOpen] = useState(false);
+  const [restoring, setRestoring] = useState(false);
 
   async function copy() {
     try {
@@ -240,12 +261,33 @@ function ActionRow({
     }
   }
 
+  async function confirmRestore() {
+    if (restoring || !actions?.onRestoreCheckpoint) return;
+    setRestoring(true);
+    try {
+      await actions.onRestoreCheckpoint(message.chat_id, message.id);
+      setRestoreOpen(false);
+    } catch (err) {
+      toast.error(err instanceof Error ? err.message : 'restore failed');
+    } finally {
+      setRestoring(false);
+    }
+  }
+
   const isAssistant = message.role === 'assistant';
   const isUser = message.role === 'user';
   const canRegen = isAssistant && message.status !== 'streaming';
   const canResend = isUser && message.status === 'complete' && !!message.content?.trim();
   const canFork = message.status === 'complete';
   const canDelete = message.status !== 'streaming';
+  // write-edit-robustness #4: show "Restore to here" only for a completed
+  // assistant message that has a checkpoint AND when the coder wired the
+  // callback. Disabled (but visible) during an active turn.
+  const canRestore =
+    isAssistant &&
+    hasCheckpoint &&
+    message.status === 'complete' &&
+    !!actions?.onRestoreCheckpoint;
 
   return (
     <>
@@ -306,6 +348,18 @@ function ActionRow({
           <Trash2 className="size-3" />
         </button>
         )}
+        {canRestore && (
+          <button
+            type="button"
+            onClick={() => setRestoreOpen(true)}
+            disabled={restoreDisabled || restoring}
+            className="inline-flex items-center justify-center size-6 rounded text-muted-foreground hover:bg-muted hover:text-foreground disabled:opacity-40 disabled:cursor-not-allowed max-md:min-h-[44px] max-md:min-w-[44px]"
+            aria-label="Restore to here"
+            title="Restore worktree to this point"
+          >
+            <History className="size-3" />
+          </button>
+        )}
       </div>
       <Dialog
         open={deleteOpen}
@@ -338,6 +392,39 @@ function ActionRow({
           </DialogFooter>
         </DialogContent>
       </Dialog>
+      <Dialog
+        open={restoreOpen}
+        onOpenChange={(open) => {
+          if (!restoring) setRestoreOpen(open);
+        }}
+      >
+        <DialogContent>
+          <DialogHeader>
+            <DialogTitle>Restore to this point?</DialogTitle>
+            <DialogDescription>
+              This resets the worktree to before this turn, removes every later
+              message in this chat, and resets the agent's session. This cannot
+              be undone.
+            </DialogDescription>
+          </DialogHeader>
+          <DialogFooter>
+            <Button
+              variant="outline"
+              onClick={() => setRestoreOpen(false)}
+              disabled={restoring}
+            >
+              Cancel
+            </Button>
+            <Button
+              variant="destructive"
+              onClick={() => void confirmRestore()}
+              disabled={restoring}
+            >
+              {restoring ? 'Restoring…' : 'Restore'}
+            </Button>
+          </DialogFooter>
+        </DialogContent>
+      </Dialog>
     </>
   );
 }
@@ -550,7 +637,15 @@ function ReasoningBlock({ text, streaming }: { text: string; streaming: boolean
   );
 }
 
-export function MessageBubble({ message, sessionChats, capHitInfo, actions, hideActions }: Props) {
+export function MessageBubble({
+  message,
+  sessionChats,
+  capHitInfo,
+  actions,
+  hideActions,
+  hasCheckpoint,
+  restoreDisabled,
+}: Props) {
   const hiddenSet = new Set(hideActions ?? []);
   // v1.11: anchored rolling summary row. Checked BEFORE the kind==='compact'
   // branch because summary=true never coexists with kind='compact' (new
@@ -652,7 +747,15 @@ export function MessageBubble({ message, sessionChats, capHitInfo, actions, hide
         </div>
       )}
       {!isStreaming && <StatsLine message={message} />}
-      {!isStreaming && hasContent && <ActionRow message={message} actions={actions} hiddenSet={hiddenSet} />}
+      {!isStreaming && hasContent && (
+        <ActionRow
+          message={message}
+          actions={actions}
+          hiddenSet={hiddenSet}
+          hasCheckpoint={hasCheckpoint}
+          restoreDisabled={restoreDisabled}
+        />
+      )}
     </div>
   );
 }