From 365d863e3ac73854d57cf54a37f9277b27d63fd6 Mon Sep 17 00:00:00 2001
From: YeonGyu-Kim <code.yeon.gyu@gmail.com>
Date: Tue, 24 Feb 2026 18:21:05 +0900
Subject: [PATCH] fix(hashline-edit): use instanceof for hash mismatch error
 detection

---
 .../hashline-edit/hashline-edit-executor.ts   |  3 ++-
 src/tools/hashline-edit/tools.test.ts         | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/src/tools/hashline-edit/hashline-edit-executor.ts b/src/tools/hashline-edit/hashline-edit-executor.ts
index bbbba4ac..e20ebbf9 100644
--- a/src/tools/hashline-edit/hashline-edit-executor.ts
+++ b/src/tools/hashline-edit/hashline-edit-executor.ts
@@ -5,6 +5,7 @@ import { countLineDiffs, generateUnifiedDiff } from "./diff-utils"
 import { canonicalizeFileText, restoreFileText } from "./file-text-canonicalization"
 import { normalizeHashlineEdits, type RawHashlineEdit } from "./normalize-edits"
 import type { HashlineEdit } from "./types"
+import { HashlineMismatchError } from "./validation"
 
 interface HashlineEditArgs {
   filePath: string
@@ -158,7 +159,7 @@ export async function executeHashlineEditTool(args: HashlineEditArgs, context: T
     return `Updated ${effectivePath}`
   } catch (error) {
     const message = error instanceof Error ? error.message : String(error)
-    if (message.toLowerCase().includes("hash")) {
+    if (error instanceof HashlineMismatchError) {
       return `Error: hash mismatch - ${message}\nTip: reuse LINE#ID entries from the latest read/edit output, or batch related edits in one call.`
     }
     return `Error: ${message}`
diff --git a/src/tools/hashline-edit/tools.test.ts b/src/tools/hashline-edit/tools.test.ts
index 46f663a3..cb76b834 100644
--- a/src/tools/hashline-edit/tools.test.ts
+++ b/src/tools/hashline-edit/tools.test.ts
@@ -103,6 +103,25 @@ describe("createHashlineEditTool", () => {
     expect(result).toContain(">>>")
   })
 
+  it("does not classify invalid pos format as hash mismatch", async () => {
+    //#given
+    const filePath = path.join(tempDir, "invalid-format.txt")
+    fs.writeFileSync(filePath, "line1\nline2")
+
+    //#when
+    const result = await tool.execute(
+      {
+        filePath,
+        edits: [{ op: "replace", pos: "42", lines: "updated" }],
+      },
+      createMockContext(),
+    )
+
+    //#then
+    expect(result).toContain("Error")
+    expect(result.toLowerCase()).not.toContain("hash mismatch")
+  })
+
   it("preserves literal backslash-n and supports string[] payload", async () => {
     //#given
     const filePath = path.join(tempDir, "test.txt")