fmt: collapse warm-resume unwrap_or_else closure per rustfmt

The 5-line spread of `.unwrap_or_else(|| { ... })` in spawn.rs (from
the bd517f28 + 65416476 warm-resume work) doesn't match rustfmt's
preference for the short form. Was blocking every merge gate since
the warm-resume fix landed.

server/src/agents/pool/start/spawn.rs

@@ -271,11 +271,9 @@ pub(super) async fn run_agent_spawn(
             // its full prior conversation restored (no need to point at
             // PLAN.md — that's the cold-start orientation path). A brief
             // "continue" nudge is all the CLI needs.
-            let resume_msg = resume_context_owned.filter(|s| !s.is_empty()).unwrap_or_else(
-                || {
-                    "Continue your prior work.".to_string()
-                },
-            );
+            let resume_msg = resume_context_owned
+                .filter(|s| !s.is_empty())
+                .unwrap_or_else(|| "Continue your prior work.".to_string());
             (resume_msg, Some(fallback))
         }
         None => {