diff --git a/src/hooks/comment-checker/hook.ts b/src/hooks/comment-checker/hook.ts
index 8989376434..ba693ef3c2 100644
--- a/src/hooks/comment-checker/hook.ts
+++ b/src/hooks/comment-checker/hook.ts
@@ -89,6 +89,11 @@ export function createCommentCheckerHooks(config?: CommentCheckerConfig) {
     ): Promise<void> => {
       debugLog("tool.execute.after:", { tool: input.tool, callID: input.callID })
 
+      if (!output.output || typeof output.output !== "string") {
+        debugLog("skipping: output.output is undefined or not a string")
+        return
+      }
+
       const toolLower = input.tool.toLowerCase()
 
       // Only skip if the output indicates a tool execution failure
diff --git a/src/hooks/edit-error-recovery/hook.ts b/src/hooks/edit-error-recovery/hook.ts
index 84ac9e9dcd..4a7fe33841 100644
--- a/src/hooks/edit-error-recovery/hook.ts
+++ b/src/hooks/edit-error-recovery/hook.ts
@@ -43,6 +43,7 @@ export function createEditErrorRecoveryHook(_ctx: PluginInput) {
       output: { title: string; output: string; metadata: unknown }
     ) => {
       if (input.tool.toLowerCase() !== "edit") return
+      if (!output.output || typeof output.output !== "string") return
 
       const outputLower = output.output.toLowerCase()
       const hasEditError = EDIT_ERROR_PATTERNS.some((pattern) =>
diff --git a/src/hooks/task-resume-info/hook.ts b/src/hooks/task-resume-info/hook.ts
index f5c0c5185b..946f9439ac 100644
--- a/src/hooks/task-resume-info/hook.ts
+++ b/src/hooks/task-resume-info/hook.ts
@@ -21,6 +21,7 @@ export function createTaskResumeInfoHook() {
     output: { title: string; output: string; metadata: unknown }
   ) => {
     if (!TARGET_TOOLS.includes(input.tool)) return
+    if (!output.output || typeof output.output !== "string") return
     if (output.output.startsWith("Error:") || output.output.startsWith("Failed")) return
     if (output.output.includes("\nto continue:")) return