Merge remote-tracking branch 'github/master' into xtr/trajectory-inspection-ui

# Conflicts:
#	packages/client/ui-primitives/src/Menu.tsx
#	packages/client/ui-trajectory/src/client/TrajectoryCell.tsx
#	packages/client/ui-trajectory/src/client/TrajectoryView.tsx
#	packages/client/ui-trajectory/tests/layout.spec.tsx
#	pnpm-lock.yaml
#	pnpm-workspace.yaml

packages/client/ui-trajectory/src/client/layout.ts

@@ -219,7 +219,9 @@ export function deriveTrajectoryLayout(input: TrajectoryLayoutInput): readonly T
     }
     if (entry.kind === 'system') {
       const { change } = entry
-      const turn = enclosingPromptTurn(nodes, change.seq, partial)
+      const turn = change.kind === 'initial'
+        ? firstVisibleTurn(nodes, partial)
+        : enclosingPromptTurn(nodes, change.seq, partial)
       pushMessage(turn, {
         absTime: finiteTime(change.time),
         cell: {
@@ -716,6 +718,20 @@ function enclosingPromptTurn(
   return partial?.turn ?? 1
 }
 
+/** Earliest raw turn represented by the selected trajectory branch. */
+function firstVisibleTurn(
+  nodes: ConversationSnapshot['nodes'],
+  partial: ConversationSnapshot['partial'],
+): number {
+  const turns = nodes.flatMap(node =>
+    (node.kind === 'assistant' || node.kind === 'steering') && node.turn > 0
+      ? [node.turn]
+      : [],
+  )
+  if (partial !== null && partial.turn > 0) turns.push(partial.turn)
+  return turns.length === 0 ? 1 : Math.min(...turns)
+}
+
 /** Copy provider usage onto a Message cell when present. */
 function attachUsage(cell: TrajectoryCellProps, usage: UsageLike | undefined): void {
   if (usage === undefined) return