diff --git a/src/Tool.ts b/src/Tool.ts
index caeac479e..889f4ba9c 100644
--- a/src/Tool.ts
+++ b/src/Tool.ts
@@ -324,7 +324,8 @@ export function filterToolProgressMessages(
 ): ProgressMessage<ToolProgressData>[] {
   return progressMessagesForMessage.filter(
     (msg): msg is ProgressMessage<ToolProgressData> =>
-      (msg.data as { type?: string })?.type !== 'hook_progress',
+      msg.data != null &&
+      (msg.data as { type?: string }).type !== 'hook_progress',
   )
 }
 
diff --git a/src/__tests__/Tool.test.ts b/src/__tests__/Tool.test.ts
index 9292459c3..3e86eb3ff 100644
--- a/src/__tests__/Tool.test.ts
+++ b/src/__tests__/Tool.test.ts
@@ -204,4 +204,19 @@ describe('filterToolProgressMessages', () => {
     const result = filterToolProgressMessages(messages)
     expect(result).toHaveLength(1)
   })
+
+  test('filters out messages with null/undefined data', () => {
+    // Regression: a progress message whose data is null used to pass through
+    // (null?.type === undefined !== 'hook_progress') and reach tool progress
+    // renderers / lookup builders, which then crashed on data.type / data.taskId
+    // field access or on 'message' in data (claude-code-best/claude-code#1330).
+    const messages = [
+      { data: null },
+      { data: undefined },
+      { data: { type: 'tool_progress', toolName: 'Bash' } },
+    ] as any[]
+    const result = filterToolProgressMessages(messages)
+    expect(result).toHaveLength(1)
+    expect((result[0]!.data as any).type).toBe('tool_progress')
+  })
 })
diff --git a/src/components/messages/AssistantToolUseMessage.tsx b/src/components/messages/AssistantToolUseMessage.tsx
index ccf55e53e..6e11a36b9 100644
--- a/src/components/messages/AssistantToolUseMessage.tsx
+++ b/src/components/messages/AssistantToolUseMessage.tsx
@@ -236,7 +236,8 @@ function renderToolUseProgressMessage(
   terminalSize: { columns: number; rows: number },
 ): React.ReactNode {
   const toolProgressMessages = progressMessagesForMessage.filter(
-    (msg): msg is ProgressMessage<ToolProgressData> => (msg.data as Record<string, unknown>).type !== 'hook_progress',
+    (msg): msg is ProgressMessage<ToolProgressData> =>
+      msg.data != null && (msg.data as Record<string, unknown>).type !== 'hook_progress',
   );
   try {
     const toolMessages =
diff --git a/src/components/messages/UserToolResultMessage/UserToolSuccessMessage.tsx b/src/components/messages/UserToolResultMessage/UserToolSuccessMessage.tsx
index bada2d9b5..cb7a52537 100644
--- a/src/components/messages/UserToolResultMessage/UserToolSuccessMessage.tsx
+++ b/src/components/messages/UserToolResultMessage/UserToolSuccessMessage.tsx
@@ -109,7 +109,16 @@ export function UserToolSuccessMessage({
   return (
     <Box flexDirection="column">
       <Box flexDirection="column" width={rendersAsAssistantText ? undefined : width}>
-        {wrappedMessage}
+        {/*
+          Tool-provided result UIs are rendered from runtime data
+          (message.toolUseResult). Resumed transcripts deserialize it via raw
+          JSON.parse (parseJSONL), so a partial/corrupt/old-format result can
+          crash renderToolResultMessage on first field access
+          (anthropics/claude-code#39817, claude-code-best/claude-code#1330).
+          Keep the result slot behind its own boundary so a bad result only
+          degrades that row instead of tearing down the whole Messages tree.
+        */}
+        <SentryErrorBoundary name="ToolResultMessage">{wrappedMessage}</SentryErrorBoundary>
         {feature('BASH_CLASSIFIER')
           ? classifierRule && (
               <MessageResponse height={1}>
diff --git a/src/utils/messages.ts b/src/utils/messages.ts
index 51884e804..1b2e0fc6d 100644
--- a/src/utils/messages.ts
+++ b/src/utils/messages.ts
@@ -1276,8 +1276,11 @@ export function buildMessageLookups(
       }
 
       // Count in-progress hooks
-      const progressData = msg.data as { type: string; hookEvent: HookEvent }
-      if (progressData.type === 'hook_progress') {
+      const progressData = msg.data as
+        | { type: string; hookEvent: HookEvent }
+        | null
+        | undefined
+      if (progressData && progressData.type === 'hook_progress') {
         const hookEvent = progressData.hookEvent
         let byHookEvent = inProgressHookCounts.get(toolUseID)
         if (!byHookEvent) {