refactor(web): extract composer text + draft persistence into a composable (#1031)

Move the composer's text ref, textarea ref, autosize helper, the per-session
draft load/save watchers, and the loadForEdit handle into useComposerDraft.
The returned text/textareaRef/autosize refs are passed straight through to the
history / slash / mention composables as their deps, so the rest of the
component is unchanged.

Composer.vue: 1987 -> 1937 lines. Adds unit tests for useComposerDraft. No
behavior change.

.changeset/web-extract-composer-draft.md

@@ -0,0 +1,5 @@
+---
+"@moonshot-ai/kimi-code": patch
+---
+
+Extract the composer's text state and per-session draft persistence into a reusable composable.

apps/kimi-web/src/components/Composer.vue

@@ -1,6 +1,6 @@
 <!-- apps/kimi-web/src/components/Composer.vue -->
 <script setup lang="ts">
-import { computed, nextTick, onMounted, onUnmounted, ref, watch } from 'vue';
+import { computed, nextTick, onMounted, onUnmounted, ref } from 'vue';
 import { useI18n } from 'vue-i18n';
 import SlashMenu from './SlashMenu.vue';
 import MentionMenu from './MentionMenu.vue';
@@ -9,10 +9,10 @@ import type { FileItem } from './MentionMenu.vue';
 import type { ActivationBadges, ConversationStatus, PermissionMode, QueuedPromptView } from '../types';
 import type { AppModel, AppSkill, ThinkingLevel } from '../api/types';
 import { modelThinkingAvailability } from '../lib/modelThinking';
-import { draftStorageKey, safeGetString, safeRemove, safeSetString } from '../lib/storage';
 import { useInputHistory } from '../composables/useInputHistory';
 import { useSlashMenu } from '../composables/useSlashMenu';
 import { useMentionMenu } from '../composables/useMentionMenu';
+import { useComposerDraft } from '../composables/useComposerDraft';
 
 // ---------------------------------------------------------------------------
 // Attachment state
@@ -101,48 +101,12 @@ const emit = defineEmits<{
 const { t } = useI18n();
 
 // ---------------------------------------------------------------------------
-// Textarea
+// Textarea + per-session draft persistence — see useComposerDraft.
 // ---------------------------------------------------------------------------
-
-// Unsent-draft persistence: the composer text is kept in localStorage PER
-// SESSION, so switching away and back (or a page refresh) restores whatever the
-// user was typing for that session. Cleared when the draft is sent/steered.
-function loadDraft(sid: string | undefined): string {
-  return safeGetString(draftStorageKey(sid)) ?? '';
-}
-function saveDraft(sid: string | undefined, value: string): void {
-  const key = draftStorageKey(sid);
-  if (value) safeSetString(key, value);
-  else safeRemove(key);
-}
-
-const text = ref(loadDraft(props.sessionId));
-const textareaRef = ref<HTMLTextAreaElement | null>(null);
-
-function autosize(): void {
-  const el = textareaRef.value;
-  if (!el) return;
-  el.style.removeProperty('height');
-}
-
-watch(text, (value) => {
-  void nextTick(autosize);
-  // Persist the live draft for the current session (empty clears the entry).
-  saveDraft(props.sessionId, value);
+const { text, textareaRef, autosize, loadForEdit } = useComposerDraft({
+  sessionId: () => props.sessionId,
 });
 
-// Switching sessions: stash the draft under the OLD session, then load the new
-// session's draft into the box.
-watch(
-  () => props.sessionId,
-  (newSid, oldSid) => {
-    if (newSid === oldSid) return;
-    saveDraft(oldSid, text.value);
-    text.value = loadDraft(newSid);
-    void nextTick(autosize);
-  },
-);
-
 // ---------------------------------------------------------------------------
 // Sent-message history recall (shell-style ↑/↓). See useInputHistory for the
 // implementation; the composer keeps the keydown orchestration (which also
@@ -362,21 +326,7 @@ onUnmounted(() => {
 // Submit / keydown
 // ---------------------------------------------------------------------------
 
-/** Imperatively load text into the box for editing (used by "edit & resend the
-    last message" after an undo, or by the dock queue panel when the user edits
-    a queued prompt). Focuses with the caret at the end. */
-function loadForEdit(value: string): void {
-  text.value = value;
-  void nextTick(() => {
-    const el = textareaRef.value;
-    if (!el) return;
-    el.focus();
-    const pos = value.length;
-    el.setSelectionRange(pos, pos);
-    autosize();
-  });
-}
-
+// loadForEdit comes from useComposerDraft (it lives next to the text state).
 defineExpose({ loadForEdit });
 
 function handleSubmit(): void {

apps/kimi-web/src/composables/useComposerDraft.ts

@@ -0,0 +1,71 @@
+// apps/kimi-web/src/composables/useComposerDraft.ts
+import { nextTick, ref, watch } from 'vue';
+import { draftStorageKey, safeGetString, safeRemove, safeSetString } from '../lib/storage';
+
+export interface ComposerDraftDeps {
+  /** Active session id — scopes the persisted draft (getter for reactivity). */
+  sessionId: () => string | undefined;
+}
+
+/**
+ * The composer's text state plus its per-session unsent-draft persistence.
+ *
+ * The draft is kept in localStorage keyed by session, so switching away and back
+ * (or a page refresh) restores whatever the user was typing for that session; it
+ * is cleared when the draft is sent/steered. This composable owns the `text`
+ * and `textarea` refs, the `autosize` helper, the draft load/save watchers, and
+ * the imperative `loadForEdit` handle exposed to the parent.
+ */
+export function useComposerDraft(deps: ComposerDraftDeps) {
+  const { sessionId } = deps;
+
+  function loadDraft(sid: string | undefined): string {
+    return safeGetString(draftStorageKey(sid)) ?? '';
+  }
+  function saveDraft(sid: string | undefined, value: string): void {
+    const key = draftStorageKey(sid);
+    if (value) safeSetString(key, value);
+    else safeRemove(key);
+  }
+
+  const text = ref(loadDraft(sessionId()));
+  const textareaRef = ref<HTMLTextAreaElement | null>(null);
+
+  function autosize(): void {
+    const el = textareaRef.value;
+    if (!el) return;
+    el.style.removeProperty('height');
+  }
+
+  watch(text, (value) => {
+    void nextTick(autosize);
+    // Persist the live draft for the current session (empty clears the entry).
+    saveDraft(sessionId(), value);
+  });
+
+  // Switching sessions: stash the draft under the OLD session, then load the new
+  // session's draft into the box.
+  watch(sessionId, (newSid, oldSid) => {
+    if (newSid === oldSid) return;
+    saveDraft(oldSid, text.value);
+    text.value = loadDraft(newSid);
+    void nextTick(autosize);
+  });
+
+  /** Imperatively load text into the box for editing (used by "edit & resend the
+      last message" after an undo, or by the dock queue panel when the user edits
+      a queued prompt). Focuses with the caret at the end. */
+  function loadForEdit(value: string): void {
+    text.value = value;
+    void nextTick(() => {
+      const el = textareaRef.value;
+      if (!el) return;
+      el.focus();
+      const pos = value.length;
+      el.setSelectionRange(pos, pos);
+      autosize();
+    });
+  }
+
+  return { text, textareaRef, autosize, loadForEdit };
+}

apps/kimi-web/test/composer-draft.test.ts

@@ -0,0 +1,106 @@
+import { afterEach, beforeEach, describe, expect, it } from 'vitest';
+import { nextTick, ref } from 'vue';
+import { useComposerDraft } from '../src/composables/useComposerDraft';
+import { draftStorageKey } from '../src/lib/storage';
+
+function memoryStorage(): Storage {
+  const map = new Map<string, string>();
+  return {
+    get length() {
+      return map.size;
+    },
+    clear: () => {
+      map.clear();
+    },
+    getItem: (key: string) => map.get(key) ?? null,
+    key: (index: number) => Array.from(map.keys())[index] ?? null,
+    removeItem: (key: string) => {
+      map.delete(key);
+    },
+    setItem: (key: string, value: string) => {
+      map.set(key, value);
+    },
+  };
+}
+
+function setup(initialSid: string | undefined) {
+  const sid = ref(initialSid);
+  const draft = useComposerDraft({ sessionId: () => sid.value });
+  return {
+    draft,
+    text: draft.text,
+    setSid: (next: string | undefined) => {
+      sid.value = next;
+    },
+  };
+}
+
+describe('useComposerDraft', () => {
+  let original: Storage | undefined;
+
+  beforeEach(() => {
+    original = (globalThis as { localStorage?: Storage }).localStorage;
+    Object.defineProperty(globalThis, 'localStorage', {
+      value: memoryStorage(),
+      configurable: true,
+      writable: true,
+    });
+  });
+
+  afterEach(() => {
+    if (original === undefined) {
+      delete (globalThis as { localStorage?: Storage }).localStorage;
+    } else {
+      Object.defineProperty(globalThis, 'localStorage', {
+        value: original,
+        configurable: true,
+        writable: true,
+      });
+    }
+  });
+
+  it('loads the stored draft for the session on init', () => {
+    globalThis.localStorage.setItem(draftStorageKey('s1'), 'saved draft');
+    const { text } = setup('s1');
+    expect(text.value).toBe('saved draft');
+  });
+
+  it('starts empty when the session has no stored draft', () => {
+    const { text } = setup('s1');
+    expect(text.value).toBe('');
+  });
+
+  it('persists the draft when the text changes', async () => {
+    const { text } = setup('s1');
+    text.value = 'hello';
+    await nextTick();
+    expect(globalThis.localStorage.getItem(draftStorageKey('s1'))).toBe('hello');
+  });
+
+  it('clears the stored draft when the text is emptied', async () => {
+    globalThis.localStorage.setItem(draftStorageKey('s1'), 'x');
+    const { text } = setup('s1');
+    text.value = '';
+    await nextTick();
+    expect(globalThis.localStorage.getItem(draftStorageKey('s1'))).toBeNull();
+  });
+
+  it('saves the old draft and loads the new one on session switch', async () => {
+    const { text, setSid } = setup('s1');
+    text.value = 'draft-s1';
+    await nextTick();
+    globalThis.localStorage.setItem(draftStorageKey('s2'), 'draft-s2');
+
+    setSid('s2');
+    await nextTick();
+
+    expect(globalThis.localStorage.getItem(draftStorageKey('s1'))).toBe('draft-s1');
+    expect(text.value).toBe('draft-s2');
+  });
+
+  it('loadForEdit replaces the text', () => {
+    const { draft } = setup('s1');
+    draft.loadForEdit('edit me');
+    expect(draft.text.value).toBe('edit me');
+  });
+});