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/components/session/project-context/DOCUMENTATION.md

@@ -60,6 +60,18 @@ Leaving the section or the project closes it, so its editor never sits over a
 list it no longer matches. Hosts that own a fullscreen plan surface (mobile)
 still pass `onOpenPlan` and keep theirs.
 
+The panel owns the only source of truth for which project a plan belongs to,
+and it never lets the editor guess. `PlanView` receives the owner as
+`savedProjectPlan={{ projectRef, planId }}` — load and autosave both go to that
+exact project. An earlier version let the editor re-derive the project from the
+current directory, which silently opened an empty document for plans stored
+under the managed Chats owner (`openchamber:chats`), for plans opened from a
+worktree the directory lookup missed, and for plan tabs restored after a
+reload. Persisted plan tabs carry `projectPlanRef` for the same reason; a saved-plan
+tab persisted with an id but no owner is dropped on rehydrate rather than
+reopened against a guessed project. A plain session plan tab legitimately has
+neither an id nor an owner and is kept.
+
 ## Pins belong to one session
 
 Notes and plans are project data, but attaching one writes its id to the current

packages/ui/src/components/session/project-context/PlansSection.tsx

@@ -5,7 +5,7 @@ import { toast } from '@/components/ui';
 import { Icon } from '@/components/icon/Icon';
 import { requestFileAccess } from '@/lib/desktop';
 import { getCurrentIntlLocale, useI18n } from '@/lib/i18n';
-import { parsePlanMarkdown, type ProjectPlanLink, type ProjectRef } from '@/lib/projectContextApi';
+import { parsePlanMarkdown, resolveProjectContextId, type ProjectPlanLink, type ProjectRef } from '@/lib/projectContextApi';
 import { runtimeFetch } from '@/lib/runtime-fetch';
 import { cn } from '@/lib/utils';
 import { useDirectoryStore } from '@/stores/useDirectoryStore';
@@ -23,8 +23,9 @@ export const PlansSection: React.FC<{
   plans: ProjectPlanLink[];
   /** Panel-wide filter, matched against plan titles. */
   query: string;
-  /** Hosts without a ContextPanel (mobile) render their own plan viewer. */
-  onOpenPlan?: (plan: { id: string; title: string }) => void;
+  /** Hosts without a ContextPanel (mobile) render their own plan viewer. The
+      plan carries its owner so the host viewer never guesses the project. */
+  onOpenPlan?: (plan: { id: string; title: string; projectRef: ProjectRef }) => void;
   pinnedPlanIds: ReadonlySet<string>;
   onTogglePinned: (planId: string, pinned: boolean) => Promise<boolean>;
 }> = ({ projectRef, plans, query, onOpenPlan, pinnedPlanIds, onTogglePinned }) => {
@@ -155,7 +156,7 @@ export const PlansSection: React.FC<{
   const handleOpenPlan = React.useCallback(
     (plan: ProjectPlanLink) => {
       if (onOpenPlan) {
-        onOpenPlan({ id: plan.id, title: plan.title });
+        onOpenPlan({ id: plan.id, title: plan.title, projectRef });
         return;
       }
       const panelDirectory = currentDirectory?.trim() || projectRef.path.trim();
@@ -165,11 +166,15 @@ export const PlansSection: React.FC<{
       openContextPanelTab(panelDirectory, {
         mode: 'plan',
         projectPlanId: plan.id,
-        dedupeKey: `plan:${plan.id}`,
+        projectPlanRef: projectRef,
+        // Storage identity is derived from the project path, not the settings
+        // id, so the tab identity uses the same derivation. Two projects
+        // sharing a settings id but not a path must not merge plan tabs.
+        dedupeKey: `plan:${resolveProjectContextId(projectRef)}:${plan.id}`,
         label: plan.title,
       });
     },
-    [currentDirectory, onOpenPlan, openContextPanelTab, projectRef.path]
+    [currentDirectory, onOpenPlan, openContextPanelTab, projectRef]
   );
 
   return (

packages/ui/src/components/session/project-context/ProjectNotesTodoPanel.tsx

@@ -29,8 +29,9 @@ interface ProjectNotesTodoPanelProps {
   canCreateWorktree?: boolean;
   onActionComplete?: () => void;
   /** When provided, opening a plan calls this instead of the desktop context
-      panel tab — hosts without ContextPanel (mobile) render their own viewer. */
-  onOpenPlan?: (plan: { id: string; title: string }) => void;
+      panel tab — hosts without ContextPanel (mobile) render their own viewer.
+      The plan carries its owner so the host's viewer cannot guess wrong. */
+  onOpenPlan?: (plan: { id: string; title: string; projectRef: ProjectRef }) => void;
   className?: string;
 }
 
@@ -501,10 +502,10 @@ export const ProjectNotesTodoPanel: React.FC<ProjectNotesTodoPanelProps> = ({
           />
         ) : null}
 
-        {activeTab === 'plans' && openPlan ? (
+        {activeTab === 'plans' && openPlan && projectRef ? (
           <React.Suspense fallback={null}>
             <PlanView
-              projectPlanId={openPlan.id}
+              savedProjectPlan={{ projectRef, planId: openPlan.id }}
               onNavigatedToChat={() => setOpenPlan(null)}
             />
           </React.Suspense>