feat(web): time stage transcript events from the stage's own start

The Transcript view is filtered to a single stage, so measure each
event's elapsed time from that stage's started_at instead of the
run's created_at. The previous behavior folded the run's
initialization wait (sandbox build, clone, devcontainer setup) into
every per-stage timestamp. Falls back to RunSummary.start_time and
then created_at for stages or runs that never ran.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/fabro-web/app/components/stage-sidebar.tsx

@@ -21,6 +21,7 @@ export interface Stage {
   duration: string;
   nodeId: string;
   visit: number;
+  startedAt: string | null;
 }
 
 export const statusConfig: Record<StageState, { icon: ComponentType<{ className?: string }>; color: string }> = {

apps/fabro-web/app/lib/stage-sidebar.test.ts

@@ -12,6 +12,7 @@ function makeStage(nodeId: string, visit: number, status: StageState): Stage {
     visit,
     status,
     duration: "--",
+    startedAt: null,
   };
 }
 

apps/fabro-web/app/lib/stage-sidebar.ts

@@ -42,6 +42,7 @@ export function mapRunStagesToSidebarStages(
       duration: stage.duration_secs != null
         ? formatDurationSecs(stage.duration_secs)
         : "--",
+      startedAt: stage.started_at ?? null,
     }));
 }
 

apps/fabro-web/app/routes/run-stages.tsx

@@ -907,7 +907,10 @@ export default function RunStages() {
     );
   }
 
-  const runStart = runQuery.data?.created_at;
+  const runStart =
+    selectedStage.startedAt ??
+    runQuery.data?.start_time ??
+    runQuery.data?.created_at;
 
   return (
     <div className="-mr-4 -mt-6 flex min-h-0 flex-1 sm:-mr-6 lg:-mr-8">