Fix infinite restart loop when effectiveCwd is undefined

When resolveThreadWorkspaceCwd returns undefined but the active session
has a persisted cwd, the comparison 'effectiveCwd !== activeSession?.cwd'
always evaluates to true, triggering a restart. However, startProviderSession
skips passing cwd when effectiveCwd is falsy, and ProviderService.startSession
backfills the old cwd from the persisted binding, creating the same mismatch
on the next turn — an infinite restart loop.

Fix: only consider cwd as changed when effectiveCwd is defined, so an
unresolved workspace does not cause spurious restarts.

Author: cursoragent

apps/server/src/orchestration/Layers/ProviderCommandReactor.ts

@@ -334,7 +334,7 @@ const make = Effect.gen(function* () {
       thread.session && thread.session.status !== "stopped" && activeSession ? thread.id : null;
     if (existingSessionThreadId) {
       const runtimeModeChanged = thread.runtimeMode !== thread.session?.runtimeMode;
-      const cwdChanged = effectiveCwd !== activeSession?.cwd;
+      const cwdChanged = effectiveCwd !== undefined && effectiveCwd !== activeSession?.cwd;
       const sessionModelSwitch =
         currentProvider === undefined
           ? "in-session"