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/hooks/use-agent-form-state.test.ts

@@ -35,7 +35,7 @@ const TEST_CLAUDE_DEFINITION: AgentProviderDefinition = {
 function makeProviderMap(
   ...definitions: AgentProviderDefinition[]
 ): Map<AgentProvider, AgentProviderDefinition> {
-  return new Map(definitions.map((d) => [d.id as AgentProvider, d]));
+  return new Map(definitions.map((d) => [d.id, d]));
 }
 
 const codexProviderMap = makeProviderMap(TEST_CODEX_DEFINITION);

packages/app/src/hooks/use-agent-form-state.ts

@@ -196,8 +196,8 @@ function resolveProvider(input: {
   if (initialValues?.provider && allowedProviderMap.has(initialValues.provider)) {
     return initialValues.provider;
   }
-  if (preferences?.provider && allowedProviderMap.has(preferences.provider as AgentProvider)) {
-    return preferences.provider as AgentProvider;
+  if (preferences?.provider && allowedProviderMap.has(preferences.provider)) {
+    return preferences.provider;
   }
   if (currentProvider && allowedProviderMap.size > 0 && !allowedProviderMap.has(currentProvider)) {
     return null;
@@ -396,7 +396,7 @@ function buildProviderDefinitionMapForStatuses(args: {
 
   const matchingProviders = new Set(
     args.snapshotEntries
-      .filter((entry) => args.statuses.has(entry.status) && entry.enabled !== false)
+      .filter((entry) => args.statuses.has(entry.status) && entry.enabled)
       .map((entry) => entry.provider),
   );
 

packages/app/src/hooks/use-audio-recorder.web.ts

@@ -341,7 +341,7 @@ export function useAudioRecorder(config?: AudioCaptureConfig) {
     return () => {
       attemptGuard.cancel();
       try {
-        void mediaRecorder.current?.stop();
+        mediaRecorder.current?.stop();
       } catch {
         // Ignore stop during unmount.
       }

packages/app/src/hooks/use-command-center.ts

@@ -332,7 +332,7 @@ export function useCommandCenter() {
         if (currentItems.length === 0) return;
         event.preventDefault();
         const index = Math.max(0, Math.min(activeIndexRef.current, currentItems.length - 1));
-        handleSelectItemRef.current(currentItems[index]!);
+        handleSelectItemRef.current(currentItems[index]);
         return;
       }
 

packages/app/src/hooks/use-dictation-audio-source.web.ts

@@ -68,7 +68,7 @@ const concatInt16 = (a: Int16Array, b: Int16Array): Int16Array => {
 const int16ToFloat32 = (input: Int16Array): Float32Array => {
   const out = new Float32Array(input.length);
   for (let i = 0; i < input.length; i += 1) {
-    out[i] = input[i]! / 32768;
+    out[i] = input[i] / 32768;
   }
   return out;
 };
@@ -209,8 +209,8 @@ export function useDictationAudioSource(config: DictationAudioSourceConfig): Dic
   const decodeAudioData = useCallback(
     async (context: AudioContext, buffer: ArrayBuffer): Promise<AudioBuffer> => {
       const maybePromise = context.decodeAudioData(buffer);
-      if (maybePromise && typeof (maybePromise as Promise<AudioBuffer>).then === "function") {
-        return maybePromise as Promise<AudioBuffer>;
+      if (maybePromise && typeof maybePromise.then === "function") {
+        return maybePromise;
       }
       return await new Promise<AudioBuffer>((resolve, reject) => {
         context.decodeAudioData(buffer, resolve, reject);
@@ -276,7 +276,7 @@ export function useDictationAudioSource(config: DictationAudioSourceConfig): Dic
       },
     });
 
-    const stream = rawStream as MediaStream;
+    const stream = rawStream;
 
     const context = new AudioContextCtor();
 
@@ -347,7 +347,7 @@ export function useDictationAudioSource(config: DictationAudioSourceConfig): Dic
 
     const recorder = new RecorderCtor(stream, {
       mimeType: "audio/webm;codecs=opus",
-    } as MediaRecorderOptions) as MediaRecorder;
+    } as MediaRecorderOptions);
 
     const recorderRefs: RecorderRefs = {
       recorder,

packages/app/src/hooks/use-keyboard-shortcuts.ts

@@ -260,7 +260,7 @@ export function useKeyboardShortcuts({
     const handleCommandCenterToggle = (event: KeyboardEvent): boolean => {
       const store = useKeyboardShortcutsStore.getState();
       if (!store.commandCenterOpen) {
-        const target = event.target instanceof Element ? (event.target as Element) : null;
+        const target = event.target instanceof Element ? event.target : null;
         const targetEl =
           target?.closest?.("textarea, input, [contenteditable='true']") ??
           (target instanceof HTMLElement ? target : null);

packages/app/src/hooks/use-pr-pane-data.ts

@@ -86,7 +86,7 @@ export function usePrPaneData({
   const checkoutPrStatus = useCheckoutPrStatusQuery({ serverId, cwd, enabled });
   const status = checkoutPrStatus.status;
   const { prNumber, repoOwner, repoName } = extractPrRepoIdentity(status);
-  const githubFeaturesEnabled = checkoutPrStatus.githubFeaturesEnabled !== false;
+  const githubFeaturesEnabled = checkoutPrStatus.githubFeaturesEnabled;
   const unsupportedKey =
     prNumber === null ? null : timelineUnsupportedKey({ serverId, cwd, prNumber });
   const timelineUnsupported = unsupportedKey ? unsupportedTimelineKeys.has(unsupportedKey) : false;
@@ -100,7 +100,7 @@ export function usePrPaneData({
     timelineUnsupported,
   });
 
-  const timelineQuery = useQuery<PullRequestTimeline, Error>({
+  const timelineQuery = useQuery<PullRequestTimeline>({
     queryKey: prPaneTimelineQueryKey({ serverId, cwd, prNumber }),
     queryFn: async () => {
       if (!daemonClient || prNumber === null || repoOwner === null || repoName === null) {

packages/app/src/hooks/use-settings.ts

@@ -235,16 +235,16 @@ export async function loadSettingsFromStorage(): Promise<Settings> {
 function pickAppSettings(stored: Partial<AppSettings>): Partial<AppSettings> {
   const result: Partial<AppSettings> = {};
   if (typeof stored.theme === "string" && VALID_THEMES.has(stored.theme)) {
-    result.theme = stored.theme as AppSettings["theme"];
+    result.theme = stored.theme;
   }
   if (stored.sendBehavior === "interrupt" || stored.sendBehavior === "queue") {
     result.sendBehavior = stored.sendBehavior;
   }
   if (
     typeof stored.serviceUrlBehavior === "string" &&
-    VALID_SERVICE_URL_BEHAVIORS.has(stored.serviceUrlBehavior as ServiceUrlBehavior)
+    VALID_SERVICE_URL_BEHAVIORS.has(stored.serviceUrlBehavior)
   ) {
-    result.serviceUrlBehavior = stored.serviceUrlBehavior as ServiceUrlBehavior;
+    result.serviceUrlBehavior = stored.serviceUrlBehavior;
   }
   return result;
 }