fix: guard output.output in tool after-hooks for MCP tools (#1720)

MCP tool responses can have undefined output.output, causing TypeError
crashes in tool.execute.after hooks.

Changes:
- comment-checker/hook.ts: guard output.output with ?? '' before toLowerCase()
- edit-error-recovery/hook.ts: guard output.output with ?? '' before toLowerCase()
- task-resume-info/hook.ts: extract output.output ?? '' into outputText before all string operations
- Added tests for undefined output.output in edit-error-recovery and task-resume-info

src/hooks/comment-checker/hook.ts

@@ -92,7 +92,7 @@ export function createCommentCheckerHooks(config?: CommentCheckerConfig) {
       const toolLower = input.tool.toLowerCase()
 
       // Only skip if the output indicates a tool execution failure
-      const outputLower = output.output.toLowerCase()
+      const outputLower = (output.output ?? "").toLowerCase()
       const isToolFailure =
         outputLower.includes("error:") ||
         outputLower.includes("failed to") ||

src/hooks/edit-error-recovery/hook.ts

@@ -44,7 +44,7 @@ export function createEditErrorRecoveryHook(_ctx: PluginInput) {
     ) => {
       if (input.tool.toLowerCase() !== "edit") return
 
-      const outputLower = output.output.toLowerCase()
+      const outputLower = (output.output ?? "").toLowerCase()
       const hasEditError = EDIT_ERROR_PATTERNS.some((pattern) =>
         outputLower.includes(pattern.toLowerCase())
       )

src/hooks/edit-error-recovery/index.test.ts

@@ -102,6 +102,23 @@ describe("createEditErrorRecoveryHook", () => {
       })
     })
 
+    describe("#given MCP tool with undefined output.output", () => {
+      describe("#when output.output is undefined", () => {
+        it("#then should not crash", async () => {
+          const input = createInput("Edit")
+          const output = {
+            title: "Edit",
+            output: undefined as unknown as string,
+            metadata: {},
+          }
+
+          await hook["tool.execute.after"](input, output)
+
+          expect(output.output).toBeUndefined()
+        })
+      })
+    })
+
     describe("#given case insensitive tool name", () => {
       describe("#when tool is 'edit' lowercase", () => {
         it("#then should still detect and append reminder", async () => {

src/hooks/task-resume-info/hook.ts

@@ -21,14 +21,15 @@ export function createTaskResumeInfoHook() {
     output: { title: string; output: string; metadata: unknown }
   ) => {
     if (!TARGET_TOOLS.includes(input.tool)) return
-    if (output.output.startsWith("Error:") || output.output.startsWith("Failed")) return
+    const outputText = output.output ?? ""
-    if (output.output.includes("\nto continue:")) return
+    if (outputText.startsWith("Error:") || outputText.startsWith("Failed")) return
+    if (outputText.includes("\nto continue:")) return
 
-    const sessionId = extractSessionId(output.output)
+    const sessionId = extractSessionId(outputText)
     if (!sessionId) return
 
     output.output =
-      output.output.trimEnd() +
+      outputText.trimEnd() +
       `\n\nto continue: task(session_id="${sessionId}", prompt="...")`
   }
 

src/hooks/task-resume-info/index.test.ts

@@ -0,0 +1,101 @@
+import { describe, it, expect } from "bun:test"
+import { createTaskResumeInfoHook } from "./index"
+
+describe("createTaskResumeInfoHook", () => {
+  const hook = createTaskResumeInfoHook()
+  const afterHook = hook["tool.execute.after"]
+
+  const createInput = (tool: string) => ({
+    tool,
+    sessionID: "test-session",
+    callID: "test-call-id",
+  })
+
+  describe("#given MCP tool with undefined output.output", () => {
+    describe("#when tool.execute.after is called", () => {
+      it("#then should not crash", async () => {
+        const input = createInput("task")
+        const output = {
+          title: "delegate_task",
+          output: undefined as unknown as string,
+          metadata: {},
+        }
+
+        await afterHook(input, output)
+
+        expect(output.output).toBeUndefined()
+      })
+    })
+  })
+
+  describe("#given non-target tool", () => {
+    describe("#when tool is not in TARGET_TOOLS", () => {
+      it("#then should not modify output", async () => {
+        const input = createInput("Read")
+        const output = {
+          title: "Read",
+          output: "some output",
+          metadata: {},
+        }
+
+        await afterHook(input, output)
+
+        expect(output.output).toBe("some output")
+      })
+    })
+  })
+
+  describe("#given target tool with session ID in output", () => {
+    describe("#when output contains a session ID", () => {
+      it("#then should append resume info", async () => {
+        const input = createInput("call_omo_agent")
+        const output = {
+          title: "delegate_task",
+          output: "Task completed.\nSession ID: ses_abc123",
+          metadata: {},
+        }
+
+        await afterHook(input, output)
+
+        expect(output.output).toContain("to continue:")
+        expect(output.output).toContain("ses_abc123")
+      })
+    })
+  })
+
+  describe("#given target tool with error output", () => {
+    describe("#when output starts with Error:", () => {
+      it("#then should not modify output", async () => {
+        const input = createInput("task")
+        const output = {
+          title: "task",
+          output: "Error: something went wrong",
+          metadata: {},
+        }
+
+        await afterHook(input, output)
+
+        expect(output.output).toBe("Error: something went wrong")
+      })
+    })
+  })
+
+  describe("#given target tool with already-continued output", () => {
+    describe("#when output already contains continuation info", () => {
+      it("#then should not add duplicate", async () => {
+        const input = createInput("task")
+        const output = {
+          title: "task",
+          output:
+            'Done.\nSession ID: ses_abc123\nto continue: task(session_id="ses_abc123", prompt="...")',
+          metadata: {},
+        }
+
+        await afterHook(input, output)
+
+        const matches = output.output.match(/to continue:/g)
+        expect(matches?.length).toBe(1)
+      })
+    })
+  })
+})