refactor(mobile): thread inspector mode is derived, not synced

apps/mobile/src/features/threads/ThreadRouteScreen.tsx

@@ -111,11 +111,6 @@ import {
 import type { ThreadInspectorTarget } from "./thread-inspector-navigation";
 import { useSelectWorkspaceDetail } from "../workspace/useSelectWorkspaceDetail";
 
-interface ThreadInspectorSelection {
-  readonly routeThreadIdentity: string | null;
-  readonly mode: ThreadInspectorMode;
-}
-
 function InspectorPaneRoleActivation() {
   useAdaptiveWorkspacePaneRole("inspector");
   return null;
@@ -435,19 +430,21 @@ function ThreadRouteContent(
   const threadId = firstRouteParam(params.threadId);
   const routeThreadIdentity =
     environmentIdRaw !== null && threadId !== null ? `${environmentIdRaw}:${threadId}` : null;
-  const [inspectorSelection, setInspectorSelection] = useState<ThreadInspectorSelection | null>(
-    () => (props.renderInspector ? { routeThreadIdentity, mode: "route" } : null),
-  );
+  // The chosen mode survives thread switches; "route" only applies while the route
+  // supplies an inspector, which is also the default whenever it does.
+  const [chosenInspectorMode, setChosenInspectorMode] = useState<ThreadInspectorMode | null>(null);
   const previewTarget = props.inspectorPresentation ? undefined : params.inspector;
   const inspectorMode = (() => {
     if (previewTarget) return "preview";
-    if (inspectorSelection?.routeThreadIdentity === routeThreadIdentity) {
-      if (inspectorSelection.mode === "files" && selectedThreadCwd === null) {
-        return null;
-      }
-      return inspectorSelection.mode;
-    }
-    return null;
+    const mode =
+      props.renderInspector === undefined
+        ? chosenInspectorMode === "route"
+          ? null
+          : chosenInspectorMode
+        : chosenInspectorMode === null || chosenInspectorMode === "route"
+          ? "route"
+          : chosenInspectorMode;
+    return mode === "files" && selectedThreadCwd === null ? null : mode;
   })();
   useEffect(() => {
     if (
@@ -468,24 +465,6 @@ function ThreadRouteContent(
     toggleAuxiliaryPane,
   ]);
 
-  useEffect(() => {
-    // oxlint-disable-next-line react/set-state-in-effect -- Inspector selection follows route ownership but keeps an inspector the user opened.
-    setInspectorSelection((current) => {
-      if (props.renderInspector === undefined) {
-        if (current === null || current.mode === "route") {
-          return null;
-        }
-        return { ...current, routeThreadIdentity };
-      }
-
-      if (current === null || current.mode === "route") {
-        return { routeThreadIdentity, mode: "route" };
-      }
-
-      return { ...current, routeThreadIdentity };
-    });
-  }, [props.renderInspector, routeThreadIdentity]);
-
   const revealPreview = useEffectEvent(() => showAuxiliaryPane("inspector"));
   useEffect(() => {
     if (previewTarget) revealPreview();
@@ -552,7 +531,7 @@ function ThreadRouteContent(
       return;
     }
     navigation.setParams({ inspector: undefined });
-    setInspectorSelection({ routeThreadIdentity, mode: "git" });
+    setChosenInspectorMode("git");
     showAuxiliaryPane("inspector");
   };
   const handleOpenFilesInspector = () => {
@@ -567,10 +546,7 @@ function ThreadRouteContent(
       return;
     }
     navigation.setParams({ inspector: undefined });
-    setInspectorSelection({
-      routeThreadIdentity,
-      mode: props.renderInspector === undefined ? "files" : "route",
-    });
+    setChosenInspectorMode(props.renderInspector === undefined ? "files" : "route");
     showAuxiliaryPane("inspector");
   };
   const handleToggleInspector = () => {