fix(desktop): open side conversations without a settled turn (#4508)

The Desktop side conversation forked the main session eagerly at mount, and only through the latest settled turn. During a session's first turn there is no settled turn, so the panel failed with "无法创建侧边对话，请稍后重试。" and stayed unusable until that turn finished.

The fork now happens on the first send, and the conversation-copy boundary can express an empty copy. `sourceTurnId` becomes optional on the copy shape; an absent value means "copy no messages", and it is accepted only for the `side_conversation` intent, enforced both at the Runtime Host protocol decoder and at the persistence lineage invariant. An empty copy inherits the source model, cwd and permission mode and records `parentSessionId`, but carries over no messages, runs, events or in-progress Todo, and fabricates no `branchOfTurnId`. `session.revision.create` still requires `sourceTurnId`, so revisions stay through-turn only and their fingerprints are unchanged.

Because the composer is live from the first frame, the "preparing" busy-tab pipeline (loading frame, `aria-busy`, drag and close disabling) has no remaining producer and is removed as part of the change. The CLI opens an empty side conversation instead of erroring, matching Desktop.

`RUNTIME_HOST_COMPATIBILITY_EPOCH` is bumped for the optional-field wire shape. No on-disk migration is needed: released versions persisted `sourceTurnId`, which is still a valid shape, so existing sessions and in-flight copy leases load unchanged.

Downgrade note: a header written by this build for an empty copy omits `sourceTurnId`, and an older release reading it throws `malformed fields`. The compatibility epoch does not cover the downgrade direction and the repo has no downgrade contract, so this is recorded as a known consequence rather than a guarded path.

Fixes #4507

Generated-by: Claude Code

Author: liuxiaocs7

apps/desktop/e2e/session-workbar.spec.ts

@@ -401,6 +401,14 @@ test('Side Chat survives collapse, confirms close, and cleans up on source switc
 
   const companion = page.locator('.maka-quote-companion');
   await expect(companion).toBeVisible();
+
+  // The companion forks lazily on the first send, not when the panel opens.
+  const sideComposer = companion.locator(COMPOSER_INPUT);
+  await sideComposer.fill('inspect this source without changing it');
+  await sideComposer.press('Enter');
+  await expect(companion).toContainText(
+    'Fake backend received: inspect this source without changing it',
+  );
   const firstForkId = await waitForCompanionForkId(page, sessionId);
   await expect(sidebar.locator(`[data-session-id=${JSON.stringify(firstForkId)}]`)).toHaveCount(0);
 
@@ -416,13 +424,6 @@ test('Side Chat survives collapse, confirms close, and cleans up on source switc
   await page.getByRole('button', { name: '展开任务工作栏' }).click();
   await expect(companion).toBeVisible();
 
-  const sideComposer = companion.locator(COMPOSER_INPUT);
-  await sideComposer.fill('inspect this source without changing it');
-  await sideComposer.press('Enter');
-  await expect(companion).toContainText(
-    'Fake backend received: inspect this source without changing it',
-  );
-
   const workbarToolbar = page.getByRole('toolbar', { name: '任务工作栏标签' }).first();
   const closeActiveSideChat = () =>
     workbarToolbar
@@ -449,6 +450,13 @@ test('Side Chat survives collapse, confirms close, and cleans up on source switc
   await expect(page.getByRole('list', { name: '打开工具' })).toBeVisible();
   await openSideChat.click();
   await expect(companion).toBeVisible();
+  // Fork again on the reopened panel's first send.
+  const reopenedComposer = companion.locator(COMPOSER_INPUT);
+  await reopenedComposer.fill('inspect once more before switching away');
+  await reopenedComposer.press('Enter');
+  await expect(companion).toContainText(
+    'Fake backend received: inspect once more before switching away',
+  );
   const secondForkId = await waitForCompanionForkId(page, sessionId);
 
   await sidebar.getByRole('button', { name: '新任务', exact: true }).click();

apps/desktop/src/main/__tests__/permission-response-ipc-boundary.test.ts

@@ -92,14 +92,28 @@ describe('permission response IPC boundary', () => {
       sourceTurnId: 'turn-2',
       turnId: 'turn-3',
     });
+    // A through-turn branch keeps its sourceTurnId; a spurious copyId is dropped.
+    assert.deepEqual(
+      normalizeBranchFromTurnInput({ sourceTurnId: 'turn-legacy', copyId: 'ignored-here' }),
+      { sourceTurnId: 'turn-legacy' },
+    );
     assert.deepEqual(
       normalizeBranchFromTurnInput({
         sourceTurnId: 'turn-3',
         name: '  Branch name  ',
         sideConversation: true,
         ignored: 1,
       }),
-      { sourceTurnId: 'turn-3', name: 'Branch name', sideConversation: true },
+      {
+        sourceTurnId: 'turn-3',
+        name: 'Branch name',
+        sideConversation: true,
+      },
+    );
+    // An empty side-conversation branch omits sourceTurnId entirely.
+    assert.deepEqual(
+      normalizeBranchFromTurnInput({ sideConversation: true }),
+      { sideConversation: true },
     );
     assert.deepEqual(
       normalizeRuntimeHostBranchFromTurnInput({
@@ -130,11 +144,23 @@ describe('permission response IPC boundary', () => {
 
     const invalidActions: Array<() => unknown> = [
       () => normalizeRegenerateTurnInput({ sourceTurnId: 'turn-1', turnId: 1 }),
-      () => normalizeBranchFromTurnInput({ sourceTurnId: 'turn-1', name: 1 }),
-      () => normalizeBranchFromTurnInput({ sourceTurnId: 'turn-1', sideConversation: 'yes' }),
-      () => normalizeBranchFromTurnInput({ sourceTurnId: 'x'.repeat(129) }),
+      () =>
+        normalizeBranchFromTurnInput({
+          sourceTurnId: 'turn-1',
+          name: 1,
+        }),
+      () =>
+        normalizeBranchFromTurnInput({
+          sourceTurnId: 'turn-1',
+          sideConversation: 'yes',
+        }),
+      () =>
+        normalizeBranchFromTurnInput({ sourceTurnId: 'x'.repeat(129) }),
       () => normalizeReviseBeforeTurnInput({ sourceTurnId: 1 }),
-      () => normalizeRuntimeHostBranchFromTurnInput({ sourceTurnId: 'turn-1' }),
+      () =>
+        normalizeRuntimeHostBranchFromTurnInput({
+          sourceTurnId: 'turn-1',
+        }),
       () => normalizeRuntimeHostReviseBeforeTurnInput({ sourceTurnId: 'turn-1', copyId: '' }),
     ];
     for (const action of invalidActions) assert.throws(action, /Invalid/);

apps/desktop/src/main/__tests__/quote-companion-disposal.test.ts

@@ -20,7 +20,10 @@
 import { deferred } from '@maka/core/test-only/async-primitives';
 import { strict as assert } from 'node:assert';
 import { afterEach, describe, it } from 'node:test';
-import type { SessionSummary, TurnRecord } from '@maka/core/session';
+import type {
+  SessionSummary,
+  TurnRecord,
+} from '@maka/core/session';
 import {
   abandonPendingCompanionCopy,
   createFakeWorkbarServices,