feat(ai): support editing sent user messages

* feat(ai): support editing sent user messages

Adds inline edit support for user messages in the AI chat panel.
Hover over a user message to reveal the edit button; confirming the
edit truncates all subsequent history and re-sends with the new content.

* fix(ai): fix IME composition and ref-focus regression in message edit

- Handle IME composition events in onEditKeydown to prevent accidental
  submission on Enter during CJK candidate selection
- Replace per-render :ref focus callback with nextTick + data attribute
  to avoid cursor jumping on every keystroke
- Extract visibleToActualIndex into aiMessageEdit.ts for testability
- Add 8 unit tests covering index mapping with contextSummary messages

* fix(ai): prevent data loss and mention pollution in message edit

- Guard connection/config before truncating messages to prevent silent data
  loss when send() bails early
- Clear selectedMentions before resend to prevent stale chips from polluting
  edited message content

apps/desktop/src/lib/__tests__/aiMessageEdit.spec.ts

@@ -0,0 +1,48 @@
+import { describe, expect, it } from "vitest";
+import { visibleToActualIndex } from "@/lib/aiMessageEdit";
+
+describe("visibleToActualIndex", () => {
+  it("maps visible index 0 to first non-summary message", () => {
+    const messages = [{ kind: undefined }, { kind: undefined }, { kind: undefined }];
+    expect(visibleToActualIndex(messages, 0)).toBe(0);
+  });
+
+  it("maps visible index 1 correctly with no summaries", () => {
+    const messages = [{ kind: undefined }, { kind: undefined }, { kind: undefined }];
+    expect(visibleToActualIndex(messages, 1)).toBe(1);
+  });
+
+  it("skips contextSummary messages when computing visible index", () => {
+    const messages = [{ kind: undefined }, { kind: "contextSummary" }, { kind: undefined }, { kind: undefined }];
+    // visible[0] → actual[0], visible[1] → actual[2], visible[2] → actual[3]
+    expect(visibleToActualIndex(messages, 0)).toBe(0);
+    expect(visibleToActualIndex(messages, 1)).toBe(2);
+    expect(visibleToActualIndex(messages, 2)).toBe(3);
+  });
+
+  it("skips multiple consecutive contextSummary messages", () => {
+    const messages = [{ kind: "contextSummary" }, { kind: "contextSummary" }, { kind: undefined }, { kind: undefined }];
+    expect(visibleToActualIndex(messages, 0)).toBe(2);
+    expect(visibleToActualIndex(messages, 1)).toBe(3);
+  });
+
+  it("returns -1 when visibleIndex is out of range", () => {
+    const messages = [{ kind: undefined }, { kind: undefined }];
+    expect(visibleToActualIndex(messages, 5)).toBe(-1);
+  });
+
+  it("returns -1 for empty messages array", () => {
+    expect(visibleToActualIndex([], 0)).toBe(-1);
+  });
+
+  it("returns -1 when all messages are contextSummary", () => {
+    const messages = [{ kind: "contextSummary" }, { kind: "contextSummary" }];
+    expect(visibleToActualIndex(messages, 0)).toBe(-1);
+  });
+
+  it("handles last visible message correctly", () => {
+    const messages = [{ kind: undefined }, { kind: "contextSummary" }, { kind: undefined }];
+    expect(visibleToActualIndex(messages, 1)).toBe(2);
+    expect(visibleToActualIndex(messages, 2)).toBe(-1);
+  });
+});

apps/desktop/src/lib/aiMessageEdit.ts

@@ -0,0 +1,19 @@
+export interface MessageWithKind {
+  kind?: string;
+}
+
+/**
+ * Maps a visible message index (contextSummary messages excluded) to the
+ * actual index in the full messages array.
+ * Returns -1 if not found.
+ */
+export function visibleToActualIndex(messages: MessageWithKind[], visibleIndex: number): number {
+  let vi = 0;
+  for (let i = 0; i < messages.length; i++) {
+    if (messages[i].kind !== "contextSummary") {
+      if (vi === visibleIndex) return i;
+      vi++;
+    }
+  }
+  return -1;
+}