Preserve source-free tasks and admitted storage choices

Keep task directories outside project provider preparation, and pass the resolved provider or explicit Core choice through source resolution, fresh-attempt checks and preparation. This prevents an installation during setup from changing the admitted storage contract.

Cover source-free project tasks, installation during setup, explicit policy preservation and managed preparation with focused heartbeat regressions. Server TypeScript check passes.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

server/src/services/plugin-workspaces.ts

@@ -185,6 +185,8 @@ export async function preparePluginWorkspace(
     existing?.metadata?.workspaceProviderRemoval
   )
     throw conflict("Workspace storage is retired or awaiting cleanup");
+  // A source-free task directory has no project storage to prepare. Existing bindings still require their owner.
+  if (!existing && (!input.projectId || !input.projectWorkspaceId)) return null;
   const saved = readWorkspaceProviderBinding(existing?.metadata);
   const mode = existing?.mode ?? input.mode,
     strategy = existing?.strategyType ?? input.strategy;