refactor(inspect-ui): rename Step.action to Step.next_action

Aligns the SPA type and consumers with the trace schema rename. The
StepSummary.action_kind/action_label labels stay unchanged since they
are derived labels, not the raw next-action.

inspect-ui/src/panels/ActionList.tsx

@@ -111,7 +111,7 @@ function renderTarget(target: string, isTag: boolean) {
 }
 
 function contentTextForStep(step: Step): string {
-  const action = step.action;
+  const action = step.next_action;
   if (!action) {
     return "";
   }
@@ -140,7 +140,7 @@ function truncateForInline(text: string): string {
 }
 
 function positionTextForStep(step: Step): string | null {
-  const action = step.action;
+  const action = step.next_action;
   if (!action) {
     return null;
   }

inspect-ui/src/routes/RunDetail.tsx

@@ -127,7 +127,7 @@ export default function RunDetail() {
     {
       id: "screenshot",
       label: "Screenshot",
-      content: <Screenshot src={beforeScreenshot} action={currentStep?.action} />,
+      content: <Screenshot src={beforeScreenshot} action={currentStep?.next_action} />,
     },
     {
       id: "snapshots",

inspect-ui/src/types.ts

@@ -125,7 +125,8 @@ export interface Step {
   timestamp: string;
   screen?: string;
   snapshots?: Record<string, unknown>;
-  action?: Action;
+  // next_action is the action chosen for the next iteration based on observing this step.
+  next_action?: Action;
   exceptions?: Exception[];
   violations?: string[];
   hierarchy?: Hierarchy;