fix(ui): open saved plans against their owning project

Saved Project knowledge plans opened as an empty editor whenever the
viewer could not resolve the owning project from the current directory:
managed chats (openchamber:chats is not a registered project), worktrees
outside the repo path, and plan tabs restored after a reload. Titles
still rendered because the list reads the manifest through the correct
owner.

- Thread the owner explicitly (savedProjectPlan = { projectRef, planId })
  from the panel, mobile surfaces, and persisted context tabs; PlanView
  no longer guesses the project.
- An unrecognized directory resolves to no owner instead of borrowing
  the active project's knowledge.
- Serialize plan writes per document (planSaveQueue) so close/switch
  within the autosave debounce no longer drops the last edits, saves
  cannot land out of order, and a recovered save clears the error banner.
- Send saved-plan contents inline in Improve/Implement prompts (they
  have no file path); disable those actions for managed-chat plans,
  which have no project directory to create a session in.
- Drop persisted plan tabs that carry an id without an owner rather than
  reopening them against a guessed project.

packages/ui/src/hooks/useProjectContextOwner.test.ts

@@ -45,4 +45,46 @@ describe('resolveProjectContextOwner', () => {
 
     expect(owner).toEqual({ id: 'openchamber', path: '/workspace/openchamber' });
   });
+
+  test('returns null for a recognized directory that owns nothing, instead of borrowing the active project', () => {
+    const owner = resolveProjectContextOwner({
+      projects,
+      worktreesByProject: new Map(),
+      directory: '/some/other/project',
+      activeProjectId: 'openchamber',
+      chatDraftOpen: false,
+      chatDraftTarget: 'project',
+      homeDirectory: '/Users/test',
+    });
+
+    expect(owner).toBeNull();
+  });
+
+  test('falls back to the active project only when there is no directory at all', () => {
+    const owner = resolveProjectContextOwner({
+      projects,
+      worktreesByProject: new Map(),
+      directory: null,
+      activeProjectId: 'openchamber',
+      chatDraftOpen: false,
+      chatDraftTarget: 'project',
+      homeDirectory: '/Users/test',
+    });
+
+    expect(owner).toEqual({ id: 'openchamber', path: '/workspace/openchamber' });
+  });
+
+  test('never falls back to the first project when the active project is unknown', () => {
+    const owner = resolveProjectContextOwner({
+      projects,
+      worktreesByProject: new Map(),
+      directory: null,
+      activeProjectId: 'missing-project',
+      chatDraftOpen: false,
+      chatDraftTarget: 'project',
+      homeDirectory: '/Users/test',
+    });
+
+    expect(owner).toBeNull();
+  });
 });

packages/ui/src/hooks/useProjectContextOwner.ts

@@ -47,7 +47,16 @@ export const resolveProjectContextOwner = ({
     return { id: sessionProject.id, path: sessionProject.path };
   }
 
-  const activeProject = projects.find((project) => project.id === activeProjectId) ?? projects[0] ?? null;
+  // A concrete directory that resolves to nothing owns nothing. Falling back
+  // to the active project here showed one project's knowledge under another
+  // project's name (the "plans open empty" bug), so the panel stays empty
+  // instead of lying. The active-project fallback is only for states with no
+  // directory at all, such as a new-session draft that has not landed yet.
+  if (normalizedDirectory) {
+    return null;
+  }
+
+  const activeProject = projects.find((project) => project.id === activeProjectId) ?? null;
   return activeProject ? { id: activeProject.id, path: activeProject.path } : null;
 };