feat(git): per-hunk stage, unstage, and discard actions in Changes view

Implements the hunk-level actions promised by the 1.13.0 changelog entry.
Each expanded file diff with 2+ hunks gets a Hunks menu (next to the
file actions) listing every hunk with its +/- counts and Stage/Unstage
+ Discard buttons, wired to the existing stageGitHunk/unstageGitHunk/
revertGitHunk API and POST /api/git/apply-hunk backend.

packages/ui/src/components/views/DiffView.tsx

@@ -34,6 +34,7 @@ import { DiffViewToggle } from '@/components/chat/message/DiffViewToggle';
 import type { DiffViewMode } from '@/components/chat/message/types';
 import { ReviewFlowDialog, type ReviewFlowExecution } from '@/components/session/ReviewFlowDialog';
 import { PierreDiffViewer } from './PierreDiffViewer';
+import { HunkActions, type HunkBusyState, type HunkDiffAction } from './git/HunkActions';
 import { useDeviceInfo } from '@/lib/device';
 import { FileTypeIcon } from '@/components/icons/FileTypeIcon';
 import { Icon } from "@/components/icon/Icon";
@@ -43,7 +44,7 @@ import { sessionEvents } from '@/lib/sessionEvents';
 import { findDiffScrollAnchor, getRestoredDiffScrollTop, type DiffScrollAnchor } from './diffScrollAnchor';
 import { useI18n } from '@/lib/i18n';
 import type { I18nKey } from '@/lib/i18n/store';
-import { fileDiffFromPatch } from '@/lib/diff/patchFileDiff';
+import { fileDiffFromPatch, extractHunkPatch } from '@/lib/diff/patchFileDiff';
 import { isVSCodeRuntime } from '@/lib/desktop';
 import { startReviewFlow } from '@/lib/reviewFlow';
 import { WALKTHROUGH_ACTION_CLASS } from '@/components/views/walkthrough/walkthroughAction';
@@ -643,6 +644,7 @@ const MultiFileDiffEntry = React.memo<MultiFileDiffEntryProps>(({
     const [diffLoadError, setDiffLoadError] = React.useState<string | null>(null);
     const [isLoading, setIsLoading] = React.useState(false);
     const [fileAction, setFileAction] = React.useState<FileDiffAction | null>(null);
+    const [hunkAction, setHunkAction] = React.useState<HunkBusyState>(null);
     const [forceRenderLarge, setForceRenderLarge] = React.useState(false);
     const [localDiffData, setLocalDiffData] = React.useState<DiffData | null>(null);
     const [stagedDiffData, setStagedDiffData] = React.useState<DiffData | null>(null);
@@ -789,6 +791,38 @@ const MultiFileDiffEntry = React.memo<MultiFileDiffEntryProps>(({
         }
     }, [directory, fetchStatus, file.path, fileAction, git, t]);
 
+    const handleHunkAction = React.useCallback(async (hunkIndex: number, action: HunkDiffAction) => {
+        if (!directory || hunkAction !== null || fileAction !== null) {
+            return;
+        }
+
+        const hunkPatch = diffData?.patch ? extractHunkPatch(diffData.patch, hunkIndex) : null;
+        if (!hunkPatch) {
+            toast.error(t('diffView.hunk.unavailable'));
+            return;
+        }
+
+        setHunkAction({ index: hunkIndex, action });
+        try {
+            const hunkMutation = action === 'stage'
+                ? git.stageGitHunk
+                : action === 'unstage'
+                    ? git.unstageGitHunk
+                    : git.revertGitHunk;
+            if (!hunkMutation) {
+                toast.error(t('diffView.hunk.unsupported'));
+                return;
+            }
+            await hunkMutation(directory, file.path, hunkPatch);
+            setDiffRetryNonce((nonce) => nonce + 1);
+            await fetchStatus(directory, git);
+        } catch (error) {
+            toast.error(error instanceof Error && error.message ? error.message : t('diffView.hunk.unavailable'));
+        } finally {
+            setHunkAction((current) => (current?.index === hunkIndex && current.action === action ? null : current));
+        }
+    }, [directory, diffData, fetchStatus, file.path, fileAction, git, hunkAction, t]);
+
     return (
         <div ref={setSectionRef} className="scroll-mt-9 border-b border-[var(--interactive-border)]/40 last:border-b-0">
             <div className="sticky top-0 z-30 border-b border-[var(--interactive-border)]/35 bg-[var(--surface-elevated)]/90 backdrop-blur-md supports-[backdrop-filter]:bg-[var(--surface-elevated)]/80">
@@ -955,7 +989,17 @@ const MultiFileDiffEntry = React.memo<MultiFileDiffEntryProps>(({
                                 wrapLines={wrapLines}
                             />
                             <div className="pointer-events-none absolute bottom-3 right-3 z-20">
-                                <div className="pointer-events-auto">
+                                <div className="pointer-events-auto flex items-center gap-1.5">
+                                    {!readOnlyActions && diffData?.patch ? (
+                                        <HunkActions
+                                            filePath={file.path}
+                                            patch={diffData.patch}
+                                            staged={staged}
+                                            busyHunk={hunkAction}
+                                            disabled={fileAction !== null || hunkAction !== null}
+                                            onAction={handleHunkAction}
+                                        />
+                                    ) : null}
                                     {!readOnlyActions ? (
                                         <FileDiffActions
                                             filePath={file.path}

packages/ui/src/components/views/git/HunkActions.tsx

@@ -0,0 +1,148 @@
+import React, { useMemo } from 'react';
+import {
+  DropdownMenu,
+  DropdownMenuContent,
+  DropdownMenuLabel,
+  DropdownMenuSeparator,
+  DropdownMenuTrigger,
+} from '@/components/ui/dropdown-menu';
+import { Icon } from '@/components/icon/Icon';
+import { useI18n } from '@/lib/i18n';
+import { splitPatchIntoHunks } from '@/lib/diff/patchFileDiff';
+
+export type HunkDiffAction = 'stage' | 'unstage' | 'discard';
+
+export type HunkBusyState = {
+  index: number;
+  action: HunkDiffAction;
+} | null;
+
+interface HunkActionsProps {
+  filePath: string;
+  patch: string;
+  staged: boolean;
+  busyHunk: HunkBusyState;
+  disabled: boolean;
+  onAction: (hunkIndex: number, action: HunkDiffAction) => void;
+}
+
+interface HunkSummary {
+  patch: string;
+  insertions: number;
+  deletions: number;
+}
+
+const summarizeHunks = (patch: string): HunkSummary[] =>
+  splitPatchIntoHunks(patch).map((hunkPatch) => {
+    let insertions = 0;
+    let deletions = 0;
+    for (const line of hunkPatch.split('\n')) {
+      if (line.startsWith('+++') || line.startsWith('---')) continue;
+      if (line.startsWith('+')) insertions += 1;
+      else if (line.startsWith('-')) deletions += 1;
+    }
+    return { patch: hunkPatch, insertions, deletions };
+  });
+
+export const HunkActions = React.memo<HunkActionsProps>(function HunkActions({
+  filePath,
+  patch,
+  staged,
+  busyHunk,
+  disabled,
+  onAction,
+}) {
+  const { t } = useI18n();
+  const hunks = useMemo(() => summarizeHunks(patch), [patch]);
+
+  if (hunks.length < 2) {
+    return null;
+  }
+
+  const primaryAction: HunkDiffAction = staged ? 'unstage' : 'stage';
+
+  return (
+    <DropdownMenu>
+      <DropdownMenuTrigger asChild>
+        <button
+          type="button"
+          disabled={disabled}
+          className="flex h-6 shrink-0 items-center gap-1 rounded-full border border-[var(--interactive-border)]/45 bg-[var(--surface-background)]/95 px-2 typography-micro font-semibold text-muted-foreground shadow-sm backdrop-blur-md hover:text-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-[var(--interactive-focus-ring)] disabled:cursor-not-allowed disabled:opacity-50"
+          aria-label={t('diffView.hunk.label')}
+          title={t('diffView.hunk.label')}
+        >
+          <Icon name="stack" className="size-3.5" />
+          <span>{t('diffView.hunk.label')} · {hunks.length}</span>
+        </button>
+      </DropdownMenuTrigger>
+      <DropdownMenuContent align="end" sideOffset={6} className="w-64">
+        <DropdownMenuLabel className="max-w-full truncate" title={filePath}>
+          {t('diffView.hunk.label')} · {filePath}
+        </DropdownMenuLabel>
+        <DropdownMenuSeparator />
+        {hunks.map((hunk, index) => {
+          const displayIndex = index + 1;
+          const busyPrimary = busyHunk?.index === index && busyHunk.action === primaryAction;
+          const busyDiscard = busyHunk?.index === index && busyHunk.action === 'discard';
+          const rowBusy = busyPrimary || busyDiscard;
+          const primaryTitle = staged
+            ? t('diffView.hunk.unstageTitle', { index: displayIndex })
+            : t('diffView.hunk.stageTitle', { index: displayIndex });
+          const discardTitle = t('diffView.hunk.discardTitle', { index: displayIndex });
+          return (
+            <div
+              key={index}
+              className="flex items-center gap-2 px-2 py-1.5"
+              aria-label={primaryTitle}
+            >
+              <span className="min-w-0 flex-1 truncate typography-ui-label text-foreground">
+                Hunk {displayIndex}
+                <span className="ml-1.5 typography-micro">
+                  {hunk.insertions > 0 ? (
+                    <span style={{ color: 'var(--status-success)' }}>+{hunk.insertions}</span>
+                  ) : null}
+                  {hunk.insertions > 0 && hunk.deletions > 0 ? (
+                    <span className="mx-0.5 text-muted-foreground">/</span>
+                  ) : null}
+                  {hunk.deletions > 0 ? (
+                    <span style={{ color: 'var(--status-error)' }}>-{hunk.deletions}</span>
+                  ) : null}
+                </span>
+              </span>
+              <button
+                type="button"
+                disabled={disabled || rowBusy}
+                onClick={() => onAction(index, primaryAction)}
+                className="flex size-6 shrink-0 items-center justify-center rounded text-muted-foreground hover:text-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-primary disabled:cursor-not-allowed disabled:opacity-50"
+                aria-label={primaryTitle}
+                title={primaryTitle}
+              >
+                {busyPrimary ? (
+                  <Icon name="loader-4" className="size-3.5 animate-spin" />
+                ) : (
+                  <Icon name="add" className="size-3.5" />
+                )}
+              </button>
+              {!staged ? (
+                <button
+                  type="button"
+                  disabled={disabled || rowBusy}
+                  onClick={() => onAction(index, 'discard')}
+                  className="flex size-6 shrink-0 items-center justify-center rounded text-muted-foreground hover:text-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-primary disabled:cursor-not-allowed disabled:opacity-50"
+                  aria-label={discardTitle}
+                  title={discardTitle}
+                >
+                  {busyDiscard ? (
+                    <Icon name="loader-4" className="size-3.5 animate-spin" />
+                  ) : (
+                    <Icon name="arrow-go-back" className="size-3.5" />
+                  )}
+                </button>
+              ) : null}
+            </div>
+          );
+        })}
+      </DropdownMenuContent>
+    </DropdownMenu>
+  );
+});