Remove unnecessary type assertions across codebase

Add oxlint-tsgolint and configure typescript/no-unnecessary-type-assertion
to flag redundant `!` and `as Foo` casts. Type-aware mode is left off by
default to keep `npm run lint` fast; the rule sits configured for when we
turn type-aware on intentionally. Auto-fix removed ~283 redundant casts;
two manual touch-ups: a real tsgolint false positive in split-container.tsx
and a stale ChildProcess import after a double-cast collapsed.

packages/app/src/components/agent-status-bar.tsx

@@ -234,7 +234,7 @@ function buildFallbackAllProviderModels(
   map.set(
     provider,
     modelOptions.map((option) => ({
-      provider: provider as AgentProvider,
+      provider: provider,
       id: option.id,
       label: option.label,
     })),

packages/app/src/components/browser-pane.electron.tsx

@@ -461,7 +461,7 @@ export function BrowserPane({
     };
     const handleFaviconUpdated = (event: Event) => {
       const favicons = Array.isArray((event as Event & { favicons?: unknown[] }).favicons)
-        ? (((event as Event & { favicons?: string[] }).favicons as string[] | undefined) ?? [])
+        ? ((event as Event & { favicons?: string[] }).favicons ?? [])
         : [];
       updateBrowserRef.current(browserIdRef.current, { faviconUrl: favicons[0] ?? null });
     };

packages/app/src/components/combined-model-selector.test.ts

@@ -63,8 +63,8 @@ describe("combined model selector helpers", () => {
       }),
     ]);
 
-    expect(matchesSearch(rows[0]!, "claude")).toBe(true);
-    expect(matchesSearch(rows[1]!, "gpt-5.4")).toBe(true);
+    expect(matchesSearch(rows[0], "claude")).toBe(true);
+    expect(matchesSearch(rows[1], "gpt-5.4")).toBe(true);
   });
 
   it("keeps the selected trigger label model-only", () => {

packages/app/src/components/combined-model-selector.tsx

@@ -622,7 +622,7 @@ export function CombinedModelSelector({
   const singleProviderView = useMemo<SelectorView | null>(() => {
     const providers = Array.from(allProviderModels.keys());
     if (providers.length !== 1) return null;
-    const providerId = providers[0]!;
+    const providerId = providers[0];
     const label = resolveProviderLabel(providerDefinitions, providerId);
     return { kind: "provider", providerId, providerLabel: label };
   }, [allProviderModels, providerDefinitions]);
@@ -655,7 +655,7 @@ export function CombinedModelSelector({
 
   const handleSelect = useCallback(
     (provider: string, modelId: string) => {
-      onSelect(provider as AgentProvider, modelId);
+      onSelect(provider, modelId);
       setIsOpen(false);
       setSearchQuery("");
     },

packages/app/src/components/composer.tsx

@@ -160,20 +160,17 @@ function removeAttachmentAtIndex<T extends ComposerAttachment>(prev: T[], index:
 }
 
 function buildCancelButtonStyle(isConnected: boolean, isCancellingAgent: boolean): object[] {
-  const disabled =
-    !isConnected || isCancellingAgent ? (styles.buttonDisabled as object) : undefined;
-  return [styles.cancelButton as object, disabled].filter((value): value is object =>
-    Boolean(value),
-  );
+  const disabled = !isConnected || isCancellingAgent ? styles.buttonDisabled : undefined;
+  return [styles.cancelButton, disabled].filter((value): value is object => Boolean(value));
 }
 
 function buildRealtimeVoiceButtonStyle(
   hovered: boolean | undefined,
   voiceButtonDisabled: boolean,
 ): object[] {
-  const hoveredStyle = hovered ? (styles.iconButtonHovered as object) : undefined;
-  const disabledStyle = voiceButtonDisabled ? (styles.buttonDisabled as object) : undefined;
-  return [styles.realtimeVoiceButton as object, hoveredStyle, disabledStyle].filter(
+  const hoveredStyle = hovered ? styles.iconButtonHovered : undefined;
+  const disabledStyle = voiceButtonDisabled ? styles.buttonDisabled : undefined;
+  return [styles.realtimeVoiceButton, hoveredStyle, disabledStyle].filter(
     (value): value is object => Boolean(value),
   );
 }

packages/app/src/components/file-explorer-pane.tsx

@@ -132,7 +132,7 @@ function TreeRowItem({
   );
 
   const handleCopy = useCallback(() => {
-    void onCopyPath(entry.path);
+    onCopyPath(entry.path);
   }, [onCopyPath, entry.path]);
 
   const handleDownload = useCallback(() => {

packages/app/src/components/project-picker-modal.tsx

@@ -29,7 +29,7 @@ interface PathRowProps {
 function PathRow({ path, active, onSelect }: PathRowProps) {
   const { theme } = useUnistyles();
   const handlePress = useCallback(() => {
-    void onSelect(path);
+    onSelect(path);
   }, [onSelect, path]);
   const pressableStyle = useCallback(
     ({ hovered = false, pressed }: PressableStateCallbackType & { hovered?: boolean }) => [
@@ -172,7 +172,7 @@ export function ProjectPickerModal() {
       if (key === "Enter") {
         event.preventDefault();
         if (options.length > 0 && activeIndex < options.length) {
-          void handleSelectPath(options[activeIndex]!);
+          void handleSelectPath(options[activeIndex]);
         } else if (query.trim()) {
           handleSubmitCustom();
         }

packages/app/src/components/provider-diagnostic-sheet.tsx

@@ -117,7 +117,7 @@ function CustomModelsSection(props: {
           },
         },
       });
-      await refresh([provider as AgentProvider]);
+      await refresh([provider]);
     },
     [patchConfig, provider, refresh],
   );
@@ -284,7 +284,7 @@ export function ProviderDiagnosticSheet({
       }
 
       try {
-        const result = await client.getProviderDiagnostic(provider as AgentProvider);
+        const result = await client.getProviderDiagnostic(provider);
         setDiagnostic(result.diagnostic);
       } catch (err) {
         setDiagnostic(err instanceof Error ? err.message : "Failed to fetch diagnostic");
@@ -308,7 +308,7 @@ export function ProviderDiagnosticSheet({
     if (!provider) {
       return;
     }
-    void Promise.all([refresh([provider as AgentProvider]), fetchDiagnostic()]).catch((err) => {
+    void Promise.all([refresh([provider]), fetchDiagnostic()]).catch((err) => {
       setDiagnostic(err instanceof Error ? err.message : "Failed to refresh provider");
     });
   }, [fetchDiagnostic, provider, refresh]);

packages/app/src/components/sidebar-workspace-list.test.tsx

@@ -351,7 +351,7 @@ describe("sidebar workspace render isolation", () => {
     act(() => {
       useSessionStore.getState().mergeWorkspaces(SERVER_ID, [
         {
-          ...createWorkspaces()[1]!,
+          ...createWorkspaces()[1],
           status: "running",
         },
       ]);

packages/app/src/components/sidebar-workspace-list.tsx

@@ -439,7 +439,7 @@ function WorkspaceStatusIndicator({
     );
   }
 
-  let KindIcon: typeof ThemedMonitor | typeof ThemedFolderGit2 | null;
+  let KindIcon: typeof ThemedMonitor | null;
   if (workspaceKind === "local_checkout") KindIcon = ThemedMonitor;
   else if (workspaceKind === "worktree") KindIcon = ThemedFolderGit2;
   else KindIcon = null;

packages/app/src/components/ui/combobox.tsx

@@ -488,7 +488,7 @@ function handleDesktopEnterKey(input: DesktopKeyHandlerInput) {
   if (input.orderedVisibleOptions.length === 0) return;
   const { activeIndex, orderedVisibleOptions } = input;
   const index = activeIndex >= 0 && activeIndex < orderedVisibleOptions.length ? activeIndex : 0;
-  input.handleSelect(orderedVisibleOptions[index]!.id);
+  input.handleSelect(orderedVisibleOptions[index].id);
 }
 
 interface FloatingSizeSetters {

packages/app/src/components/use-web-scrollbar.tsx

@@ -140,9 +140,9 @@ export function useWebScrollViewScrollbar(
       const scrollable = scrollableRef.current;
       if (!scrollable) return;
       if ("scrollToOffset" in scrollable) {
-        (scrollable as FlatList).scrollToOffset({ offset, animated: false });
+        scrollable.scrollToOffset({ offset, animated: false });
       } else {
-        (scrollable as ScrollView).scrollTo({ y: offset, animated: false });
+        scrollable.scrollTo({ y: offset, animated: false });
       }
     },
     [scrollableRef],