diff --git a/packages/core/src/utils/bfsFileSearch.ts b/packages/core/src/utils/bfsFileSearch.ts
index 460abfec27..0686ef2f5a 100644
--- a/packages/core/src/utils/bfsFileSearch.ts
+++ b/packages/core/src/utils/bfsFileSearch.ts
@@ -10,6 +10,7 @@ import * as path from 'node:path';
 import type { FileDiscoveryService } from '../services/fileDiscoveryService.js';
 import type { FileFilteringOptions } from '../config/constants.js';
 import { debugLogger } from './debugLogger.js';
+import { getErrorMessage } from './errors.js';
 // Simple console logger for now.
 // TODO: Integrate with a more robust server-side logger.
 const logger = {
@@ -80,10 +81,8 @@ export async function bfsFileSearch(
         return { currentDir, entries };
       } catch (error) {
         // Warn user that a directory could not be read, as this affects search results.
-        // eslint-disable-next-line @typescript-eslint/no-unsafe-type-assertion
-        const message = (error as Error)?.message ?? 'Unknown error';
         debugLogger.warn(
-          `[WARN] Skipping unreadable directory: ${currentDir} (${message})`,
+          `[WARN] Skipping unreadable directory: ${currentDir} (${getErrorMessage(error)})`,
         );
         if (debug) {
           logger.debug(`Full error for ${currentDir}:`, error);
@@ -154,10 +153,8 @@ export function bfsFileSearchSync(
           foundFiles,
         );
       } catch (error) {
-        // eslint-disable-next-line @typescript-eslint/no-unsafe-type-assertion
-        const message = (error as Error)?.message ?? 'Unknown error';
         debugLogger.warn(
-          `[WARN] Skipping unreadable directory: ${currentDir} (${message})`,
+          `[WARN] Skipping unreadable directory: ${currentDir} (${getErrorMessage(error)})`,
         );
       }
     }
diff --git a/packages/core/src/utils/checkpointUtils.ts b/packages/core/src/utils/checkpointUtils.ts
index 97a06673ff..0aab0a2a2f 100644
--- a/packages/core/src/utils/checkpointUtils.ts
+++ b/packages/core/src/utils/checkpointUtils.ts
@@ -49,12 +49,12 @@ export function generateCheckpointFileName(
   toolCall: ToolCallRequestInfo,
 ): string | null {
   const toolArgs = toolCall.args;
-  // eslint-disable-next-line @typescript-eslint/no-unsafe-type-assertion
-  const toolFilePath = toolArgs['file_path'] as string;
+  const rawFilePath = toolArgs['file_path'];
 
-  if (!toolFilePath) {
+  if (typeof rawFilePath !== 'string' || !rawFilePath) {
     return null;
   }
+  const toolFilePath = rawFilePath;
 
   const timestamp = new Date()
     .toISOString()
@@ -168,11 +168,14 @@ export function getCheckpointInfoList(
 
   for (const [file, content] of checkpointFiles) {
     try {
-      // eslint-disable-next-line @typescript-eslint/no-unsafe-type-assertion
-      const toolCallData = JSON.parse(content) as ToolCallData;
-      if (toolCallData.messageId) {
+      const parsed: unknown = JSON.parse(content);
+      const result = z
+        .object({ messageId: z.string() })
+        .passthrough()
+        .safeParse(parsed);
+      if (result.success) {
         checkpointInfoList.push({
-          messageId: toolCallData.messageId,
+          messageId: result.data.messageId,
           checkpoint: file.replace('.json', ''),
         });
       }