fix(ui): include stage in leaf coalesce key

PR-Agent flagged that the leaf coalesceKey omitted `stage`, so two
adjacent no-requestId logs differing only by stage (e.g. one logging
`route` and the next `dispatch`) would merge into a single `×2`
row, hiding a distinct entry.

Add `stage` to the coalesce tuple. New unit test asserts that two
leaves identical except for stage stay as separate rows.

Refs #1138, #1151

ui/src/components/logs/derive-trace-groups.ts

@@ -33,6 +33,7 @@ function coalesceKey(entry: LogsEntry): string {
   return [
     entry.event ?? '',
     entry.message ?? '',
+    entry.stage ?? '',
     entry.module ?? entry.source ?? '',
     entry.level,
     entry.requestId ?? '',

ui/tests/unit/ui/components/logs-derive-trace-groups.test.ts

@@ -119,6 +119,17 @@ describe('deriveTraceGroups', () => {
     expect(leaves.every((l) => l.repeatCount === undefined)).toBe(true);
   });
 
+  it('keeps adjacent leaves with different stages as separate rows (round-6 fix)', () => {
+    const result = deriveTraceGroups(
+      leafEntries(
+        { id: '1', timestamp: 't1', event: 'e', message: 'm', stage: 'route' },
+        { id: '2', timestamp: 't2', event: 'e', message: 'm', stage: 'dispatch' }
+      )
+    );
+    expect(result).toHaveLength(2);
+    expect(result.every((r) => r.kind === 'leaf' && r.repeatCount === undefined)).toBe(true);
+  });
+
   it('keeps adjacent leaves with different messages as separate rows', () => {
     const result = deriveTraceGroups(
       leafEntries(