@@ -215,6 +215,20 @@ const SUBAGENT_REPORTED_EVENT_TYPES = [
 ] as const;
 const TODO_EVENT_TYPES = ["todo_updated"] as const;
 
+/**
+ * `Array.prototype.includes` accepts any value, but these literal tuples are what
+ * make a dispatch branch exhaustive, so membership has to narrow `type` instead of
+ * merely comparing it — `type && TODO_EVENT_TYPES.includes(type)` still hands a
+ * plain `string` to a `"todo_updated"` parameter. A frame carrying no event name
+ * belongs to no branch, which is what `includes(undefined)` already answered.
+ */
+function isEventTypeOf<T extends string>(
+  type: string | undefined,
+  allowed: readonly T[],
+): type is T {
+  return type !== undefined && (allowed as readonly string[]).includes(type);
+}
+
 function terminalSubagentStatus(
   type: string,
   data: Record<string, unknown>,
@@ -231,11 +245,11 @@ export function reduceWebuiWorkspaceProgressEvent(
   sessionId?: string,
 ): WebuiWorkspaceProgressState {
   const type = eventType(value);
-  if (TODO_EVENT_TYPES.includes(type)) {
+  if (isEventTypeOf(type, TODO_EVENT_TYPES)) {
     const todos = normalizeTodos(value.todos ?? eventData(value).todos);
     return todos ? { ...state, todos, hasTodoSnapshot: true } : state;
   }
-  if (SUBAGENT_SPAWN_EVENT_TYPES.includes(type)) {
+  if (isEventTypeOf(type, SUBAGENT_SPAWN_EVENT_TYPES)) {
     const subagent = subagentFromEvent(value, sessionId);
     return subagent
       ? {
@@ -245,7 +259,7 @@ export function reduceWebuiWorkspaceProgressEvent(
         }
       : state;
   }
-  if (SUBAGENT_STATUS_EVENT_TYPES.includes(type)) {
+  if (isEventTypeOf(type, SUBAGENT_STATUS_EVENT_TYPES)) {
     const data = eventData(value);
     const childSessionId = stringValue(data, ["sessionId", "session_id"]);
     if (!childSessionId) return state;
@@ -262,7 +276,7 @@ export function reduceWebuiWorkspaceProgressEvent(
         hasSubagentSnapshot: true,
       };
   }
-  if (SUBAGENT_REPORTED_EVENT_TYPES.includes(type)) {
+  if (isEventTypeOf(type, SUBAGENT_REPORTED_EVENT_TYPES)) {
     const data = eventData(value);
     const childSessionId = stringValue(data, ["sessionId", "session_id"]);
     const existing = childSessionId
@@ -329,8 +343,12 @@ function applyTodoToolCalls(
   message: WebuiClientMessage | Record<string, unknown>,
 ): WebuiWorkspaceProgressState {
   const loose = message as Record<string, unknown>;
+  // `message` is a union, and its `Record<string, unknown>` arm types `toolCalls`
+  // as `unknown` — so `message.toolCalls ?? []` leaves a non-iterable on the
+  // right-hand side. Read the declared field through the same `Array.isArray`
+  // guard as the snake_case one below it.
   const calls = [
-    ...(message.toolCalls ?? []),
+    ...(Array.isArray(message.toolCalls) ? message.toolCalls : []),
     ...(Array.isArray(loose.tool_calls) ? loose.tool_calls : []),
   ];
   let next = state;
 
@@ -1,8 +1,32 @@
 {
-  "extends": "../../tsconfig.node.json",
+  "extends": "./tsconfig.paths.json",
   "compilerOptions": {
     "composite": false,
-    "rootDir": "."
+    // The path map resolves workspace packages to their TypeScript source, so the
+    // program legitimately spans the repository rather than just this package.
+    "rootDir": "../..",
+    // `tsconfig.node.json` turns these on, but the workspace packages and the
+    // vendored `third_party` sources this program pulls in are held to `strict`
+    // without them — `tsconfig.standalone.json`, `pi-mono/tsconfig.base.json` and
+    // `sandbox-runtime/tsconfig.json` all leave them off. TypeScript has no
+    // per-directory options, so the program-wide value has to match the standard
+    // its own inputs are actually written to.
+    "noUncheckedIndexedAccess": false,
+    "noImplicitOverride": false,
+    // `third_party/pi-mono`'s TUI source uses the ES2024 `v` regular-expression
+    // flag, which the inherited ES2022 target rejects.
+    "target": "ES2024",
+    // The path map points at `.ts` entry points, which TypeScript only accepts when
+    // emitting is off. Every leaf config in this chain sets `noEmit`.
+    "allowImportingTsExtensions": true
   },
+  // `third_party/pi-mono` reaches `highlight.js` through a deep subpath that
+  // bypasses the package's own `types`, and ships an ambient declaration for it.
+  // Ambient declarations only take effect when the file is part of the program, and
+  // `extends` replaces `include` wholesale, so it cannot ride along there. `files`
+  // is inherited instead, and unions with each leaf's own `include`.
+  "files": [
+    "../../third_party/pi-mono/packages/coding-agent/src/utils/highlight-js-lib-index.d.ts"
+  ],
   "include": ["src/**/*.ts", "src/**/*.tsx"]
 }