Key workspace status and ownership by ID, not directory

Multiple workspaces can share one checkout directory. Agent and terminal
status, sidebar tabs, and ownership now attribute strictly by workspace ID,
so a running or blocked agent in one workspace no longer shows up on its
same-directory siblings.

A one-time startup migration backfills workspace IDs onto legacy agents, and
every agent and terminal is created with one thereafter. Directory lookups
remain only for genuinely folder-derived git facts (branch, diff) and the
archive-by-path adapter.

packages/app/src/workspace/use-workspace-archive.ts

@@ -32,6 +32,9 @@ export function useIsLastWorktreeReference(workspace: SidebarWorkspaceEntry): bo
       if (candidate.id === workspace.workspaceId) {
         continue;
       }
+      // Git-fact: comparing directories to detect a sibling worktree reference on
+      // disk, not attributing ownership. The disk-deletion decision is about the
+      // backing directory, which same-cwd siblings genuinely share.
       if (normalizeWorkspacePath(candidate.workspaceDirectory) === directory) {
         return false;
       }

packages/app/src/workspace/workspace-archive.test.ts

@@ -51,7 +51,6 @@ function target(input?: Partial<WorkspaceArchiveTarget>): WorkspaceArchiveTarget
   return {
     serverId: SERVER_ID,
     workspaceId: base.id,
-    workspaceDirectory: base.workspaceDirectory,
     ...input,
   };
 }
@@ -107,7 +106,6 @@ describe("archiveWorkspaceOptimistically", () => {
       isWorkspaceArchivePending({
         serverId: SERVER_ID,
         workspaceId: archived.id,
-        workspaceDirectory: archived.workspaceDirectory,
       }),
     ).toBe(true);
 
@@ -178,10 +176,7 @@ describe("archiveWorkspacesOptimistically", () => {
 
     const failures = await archiveWorkspacesOptimistically({
       client,
-      workspaces: [
-        target({ workspaceId: first.id, workspaceDirectory: first.workspaceDirectory }),
-        target({ workspaceId: second.id, workspaceDirectory: second.workspaceDirectory }),
-      ],
+      workspaces: [target({ workspaceId: first.id }), target({ workspaceId: second.id })],
     });
 
     expect(failures).toHaveLength(1);

packages/app/src/workspace/workspace-archive.ts

@@ -8,7 +8,6 @@ import { resolveWorkspaceMapKeyByIdentity } from "@/utils/workspace-identity";
 export interface WorkspaceArchiveTarget {
   serverId: string;
   workspaceId: string;
-  workspaceDirectory?: string | null;
 }
 
 interface WorkspaceArchiveClient {
@@ -46,7 +45,6 @@ function hideWorkspaceOptimistically(
   markWorkspaceArchivePending({
     serverId: workspace.serverId,
     workspaceId: workspace.workspaceId,
-    workspaceDirectory: workspace.workspaceDirectory,
   });
   useSessionStore.getState().removeWorkspace(workspace.serverId, workspace.workspaceId);
   return { workspace: snapshot };