Make workspace IDs opaque, independent of the filesystem path (#1503)

* Make workspace IDs opaque, independent of the filesystem path

Workspace IDs were the resolved checkout/worktree path, so code could
treat an ID as a path: prefix matching, deriving directories from it,
falling back to a path when a lookup missed. IDs are now opaque -
compared only by exact equality and never used as a path. Anything
path-shaped resolves the workspace record first and reads its cwd.

New workspaces get a generated `wks_` ID; existing path-shaped IDs are
read from disk and never regenerated, so there is no migration and no
change to the wire or persisted schemas. Groundwork for running
multiple workspaces in a single directory.

* Keep attachment scope key stable and align refetch test

The attachment scope key keeps `workspace=` instead of `wsid=` so existing
persisted drafts are not orphaned; the rename was cosmetic. The SDK refetch
test no longer asserts a filter, matching refetch fetching one page and
selecting by id client-side.

* Fix live agent updates in directories without a registered workspace

The opaque-ID work removed buildProjectPlacementForCwd's directory
fallback, so an agent running in a folder with no registered workspace
(e.g. a fresh non-git dir) produced a null placement. forwardAgentUpdate
then threw "Workspace not found", the error was swallowed by its catch,
and no agent_update was emitted — live model/thinking switches and status
updates silently stopped. Caught by the live-preferences e2e suite.

The fallback builds a directory-scoped project placement keyed by the
path. That key is a project grouping key (non-git projects group by
path), not a workspace id, so it stays within the opaque-id rule.

* Always run server worktree archive, even without a resolved workspace

Archiving bailed out entirely when the workspace was not found in the
client store, so a race or stale state could make "archive" do nothing
server-side with only a console.warn. The server archive is keyed by
worktreePath, which is always available, so it now runs regardless; only
the optimistic client-side updates (keyed by workspace id) are gated on
the workspace being resolved.

* Expect a directory-scoped placement for unregistered agent dirs

This unit test asserted the no-placement behavior reverted in the live
agent-update fix, which had broken live model/thinking switching. Update
it to expect the directory-scoped placement now emitted for an agent in a
directory with no registered workspace.

* Fix opaque workspace routing in app E2E

* Preserve workspace IDs during partial bootstrap

* Fix archive flows for opaque workspace IDs

* Stop treating opaque workspace IDs as filesystem paths

Workspace IDs are opaque (wks_<hex>), but several call sites still passed
the id where a directory was expected, which broke those flows for opaque
IDs. The branch switcher sent the id as a cwd to branch/stash/checkout git
operations, and server archive/reconcile cleanup keyed git-watch and
subscription teardown by id, leaking that state.

Git and filesystem operations now take the workspace directory; the opaque
id is used only for identity and cache keys. Archive/reconcile cleanup
routes through a single teardownArchivedWorkspace helper that keeps the key
split explicit: runtime store by id, git watch and subscription by cwd.
Path-derived grouping keys are renamed to directory keys, and the helpers
are split into workspace-identity and workspace-directory so the id-vs-path
boundary is obvious.

packages/app/src/panels/browser-panel.tsx

@@ -6,7 +6,7 @@ import { BrowserPane } from "@/components/browser-pane";
 import { usePaneContext, usePaneFocus } from "@/panels/pane-context";
 import type { PanelDescriptor, PanelIconProps, PanelRegistration } from "@/panels/panel-registry";
 import { useBrowserStore } from "@/stores/browser-store";
-import { useWorkspaceExecutionAuthority } from "@/stores/session-store-hooks";
+import { useWorkspaceDirectory } from "@/stores/session-store-hooks";
 
 function getBrowserLabel(input: { title: string; url: string }): string {
   const title = input.title.trim();
@@ -55,8 +55,7 @@ function useBrowserPanelDescriptor(target: {
 function BrowserPanel() {
   const { serverId, workspaceId, target } = usePaneContext();
   const { focusPane, isInteractive } = usePaneFocus();
-  const workspaceAuthority = useWorkspaceExecutionAuthority(serverId, workspaceId)!;
-  const cwd = workspaceAuthority.ok ? workspaceAuthority.authority.workspaceDirectory : null;
+  const cwd = useWorkspaceDirectory(serverId, workspaceId);
   invariant(target.kind === "browser", "BrowserPanel requires browser target");
   return (
     <BrowserPane