Default JSON log-line viewer nodes to collapsed

A log line whose text parses as JSON was rendering every nested node
fully expanded, dumping large payloads into the timeline instead of a
collapsed summary the user opts into expanding.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TeyhRfMYjMditek6geDRoQ

src/engine/handle.rs

@@ -100,31 +100,31 @@ impl EngineHandle {
     }
 }
 
-pub fn spawn(settings: SettingsHandle, channel_capacity: usize) -> EngineHandle {
+/// Builds the handle/receiver/writer triple shared by `spawn` and, in tests, by callers that
+/// want the raw receiver without an actor loop draining it.
+fn new_channel_and_handle(
+    channel_capacity: usize,
+) -> (EngineHandle, mpsc::Receiver<EngineMessage>, IndexWriter) {
     let (tx, rx) = mpsc::channel(channel_capacity);
     let (write, read) = left_right::new::<EngineSnapshot, EngineOp>();
     let reader = IndexReader {
         factory: read.factory(),
     };
-    tokio::spawn(run(rx, settings, IndexWriter { handle: write }));
-    EngineHandle { tx, reader }
+    (EngineHandle { tx, reader }, rx, IndexWriter { handle: write })
+}
+
+pub fn spawn(settings: SettingsHandle, channel_capacity: usize) -> EngineHandle {
+    let (handle, rx, write) = new_channel_and_handle(channel_capacity);
+    tokio::spawn(run(rx, settings, write));
+    handle
 }
 
 #[cfg(test)]
 pub(crate) fn test_handle(
     channel_capacity: usize,
 ) -> (EngineHandle, mpsc::Receiver<EngineMessage>) {
-    let (tx, rx) = mpsc::channel(channel_capacity);
-    let (_write, read) = left_right::new::<EngineSnapshot, EngineOp>();
-    (
-        EngineHandle {
-            tx,
-            reader: IndexReader {
-                factory: read.factory(),
-            },
-        },
-        rx,
-    )
+    let (handle, rx, _write) = new_channel_and_handle(channel_capacity);
+    (handle, rx)
 }
 
 async fn run(