feat(knowledge): rebuild the project notes panel as Project knowledge (#2973)

The panel stored notes, todos and plans inside one shared JSON file that
six unrelated domains also wrote to, synchronised itself through window
CustomEvents, and could only read plans. It is now Project knowledge:
server-owned storage with explicit routes, a store with rollback, a
section sidebar, plans that open and edit in place, and search across
all of it.

Notes and plans the user pins travel with every message sent in that
project. Pinning is project state, not an attachment to one message, so
it holds until unpinned and the work status panel names what is riding
along and can detach it.

Agent memory is added alongside, in two scopes: what is true about the
user, and what is true about this codebase. The split is not cosmetic —
a wrong project fact costs one project and is noticed, while a wrong
global fact quietly shapes every session everywhere and the user has no
code to check it against. It stays separate from notes so an agent
mistake cannot land in what the user wrote. Sessions receive an index of
titles only; bodies are read on demand, because an index carrying full
text grows until it crowds out the conversation.

Deciding what a session must be told, and whether it has been told, now
lives on the server. The client owned it before, which meant sessions
started without a UI — scheduled tasks, sessions the agent dispatches —
received nothing at all, and a tab's record of what it had sent outlived
the conversation: after compaction the agent no longer held the block
while the tab went on believing it did. What was delivered is recorded
in the session's own metadata, and compaction restores it through the
runtime that already restores pinned messages, in the same turn.

Agent memory ships dark behind OPENCHAMBER_MEMORY_ENABLE: unset, there
is no tool, no routes, no session index, no settings row and no panel
tab. Absent rather than switched off, so nothing invites turning on a
feature that has not been announced. Pinned notes and plans are
unaffected and ship as normal.

packages/ui/src/apps/MobileApp.tsx

@@ -109,7 +109,7 @@ const MobileShell: React.FC<{ onActiveConnectionDeleted: () => void }> = ({ onAc
   const [workspaceTab, setWorkspaceTab] = React.useState<MobileWorkspaceTab>('changes');
   // A plan opened from the workspace drawer's Notes tab, shown as a fullscreen
   // layer on top of it (back returns to the notes).
-  const [openPlan, setOpenPlan] = React.useState<{ path: string; title: string } | null>(null);
+  const [openPlan, setOpenPlan] = React.useState<{ id: string; title: string } | null>(null);
   const [settingsInitialMobileStage, setSettingsInitialMobileStage] = React.useState<'nav' | 'page-content'>('nav');
   // When set, the Changes surface opens directly into the per-file diff for this path.
   const [pendingChangesDiff, setPendingChangesDiff] = React.useState<{ path: string; staged: boolean } | null>(null);
@@ -540,7 +540,7 @@ const MobileShell: React.FC<{ onActiveConnectionDeleted: () => void }> = ({ onAc
           >
             <ErrorBoundary>
               <PlanView
-                targetPath={openPlan.path}
+                projectPlanId={openPlan.id}
                 onNavigatedToChat={() => {
                   closeSurface();
                   closeWorkspace();

packages/ui/src/apps/MobileWorkspaceDrawer.tsx

@@ -105,7 +105,7 @@ export const MobileWorkspaceDrawer: React.FC<{
   /** When set, the Changes tab opens directly into the per-file diff. */
   pendingChangesDiff: { path: string; staged: boolean } | null;
   /** Notes tab: opens a plan fullscreen (layered above the drawer). */
-  onOpenPlan: (plan: { path: string; title: string }) => void;
+  onOpenPlan: (plan: { id: string; title: string }) => void;
   /** MCP tab: jump to the MCP settings page pre-seeded with a new server draft. */
   onOpenMcpSettings: () => void;
   variant?: 'drawer' | 'panel';

packages/ui/src/apps/runtimeEndpointReset.ts

@@ -3,6 +3,7 @@ import type { RuntimeEndpointChangedDetail } from '@/lib/runtime-switch';
 import { disposeTerminalInputTransport } from '@/lib/terminalApi';
 import { useConfigStore } from '@/stores/useConfigStore';
 import { useProjectsStore } from '@/stores/useProjectsStore';
+import { useProjectContextStore } from '@/stores/useProjectContextStore';
 import { useGlobalSessionsStore } from '@/stores/useGlobalSessionsStore';
 import { useAutoReviewStore } from '@/stores/useAutoReviewStore';
 import { useUIStore } from '@/stores/useUIStore';
@@ -52,6 +53,9 @@ export const resetAppForRuntimeEndpointChange = (detail: RuntimeEndpointChangedD
     lastDisconnectReason: null,
   });
   useProjectsStore.getState().resetForRuntimeSwitch();
+  // Notes, todos, plans and the pinned-context bookkeeping are keyed by a
+  // path-derived project id, which two runtimes can collide on.
+  useProjectContextStore.getState().reset();
   // Cross-project session list (mobile sessions sheet & co) belongs to the
   // previous instance — drop it so stale sessions can't linger after a switch.
   useGlobalSessionsStore.getState().resetForRuntimeSwitch();