fix: resolve errand worktree path for sendMessage instead of using agent-workdirs

Errand agents are spawned in the errand's git worktree (managed by
SimpleGitWorktreeManager), not in agent-workdirs/<alias>/.
sendUserMessage was deriving the cwd from worktreeId which pointed to
the non-existent agent-workdirs path. Now the errand.sendMessage
procedure resolves the actual worktree path and passes it through.

apps/server/trpc/routers/errand.ts

@@ -397,7 +397,23 @@ export function errandProcedures(publicProcedure: ProcedureBuilder) {
             });
           }
 
-          await agentManager.sendUserMessage(errand.agentId, input.message);
+          // Resolve errand worktree path — errand agents don't use agent-workdirs/
+          let worktreePath: string | undefined;
+          if (errand.projectId) {
+            const project = await requireProjectRepository(ctx).findById(errand.projectId);
+            if (project) {
+              try {
+                const clonePath = await resolveClonePath(project, ctx);
+                const wm = new SimpleGitWorktreeManager(clonePath);
+                const wt = await wm.get(errand.id);
+                if (wt) worktreePath = wt.path;
+              } catch {
+                // Fall through — sendUserMessage will use default path
+              }
+            }
+          }
+
+          await agentManager.sendUserMessage(errand.agentId, input.message, worktreePath);
           return { success: true };
         }),