From a2ec01e12fb9088e5ee60bc7e3eb5070c034f508 Mon Sep 17 00:00:00 2001
From: Danila Poyarkov <dev@dannote.net>
Date: Sat, 18 Apr 2026 19:29:23 +0300
Subject: [PATCH] fix(coding-agent): coerce stringified JSON edits in edit tool
 (#3370)

Some models (Opus 4.6, GLM-5.1) send the edits parameter as a JSON
string instead of a parsed array. This fails AJV validation with
'must be array' and models fall back to sed/python.

Parse stringified edits in prepareEditArguments before validation.
---
 packages/coding-agent/src/core/tools/edit.ts  | 22 +++++++++++-----
 .../test/edit-tool-legacy-input.test.ts       | 26 +++++++++++++++++++
 2 files changed, 42 insertions(+), 6 deletions(-)

diff --git a/packages/coding-agent/src/core/tools/edit.ts b/packages/coding-agent/src/core/tools/edit.ts
index aac8cbbe9..e4bba04de 100644
--- a/packages/coding-agent/src/core/tools/edit.ts
+++ b/packages/coding-agent/src/core/tools/edit.ts
@@ -92,14 +92,24 @@ function prepareEditArguments(input: unknown): EditToolInput {
 		return input as EditToolInput;
 	}
 
-	const args = input as LegacyEditToolInput;
-	if (typeof args.oldText !== "string" || typeof args.newText !== "string") {
-		return input as EditToolInput;
+	const args = input as Record<string, unknown>;
+
+	// Some models (Opus 4.6, GLM-5.1) send edits as a JSON string instead of an array
+	if (typeof args.edits === "string") {
+		try {
+			const parsed = JSON.parse(args.edits);
+			if (Array.isArray(parsed)) args.edits = parsed;
+		} catch {}
 	}
 
-	const edits = Array.isArray(args.edits) ? [...args.edits] : [];
-	edits.push({ oldText: args.oldText, newText: args.newText });
-	const { oldText: _oldText, newText: _newText, ...rest } = args;
+	const legacy = args as LegacyEditToolInput;
+	if (typeof legacy.oldText !== "string" || typeof legacy.newText !== "string") {
+		return args as EditToolInput;
+	}
+
+	const edits = Array.isArray(legacy.edits) ? [...legacy.edits] : [];
+	edits.push({ oldText: legacy.oldText, newText: legacy.newText });
+	const { oldText: _oldText, newText: _newText, ...rest } = legacy;
 	return { ...rest, edits } as EditToolInput;
 }
 
diff --git a/packages/coding-agent/test/edit-tool-legacy-input.test.ts b/packages/coding-agent/test/edit-tool-legacy-input.test.ts
index d78acc655..13a8bbeb5 100644
--- a/packages/coding-agent/test/edit-tool-legacy-input.test.ts
+++ b/packages/coding-agent/test/edit-tool-legacy-input.test.ts
@@ -88,3 +88,29 @@ describe("edit tool prepareArguments", () => {
 		expect(await readFile(filePath, "utf8")).toBe("after\n");
 	});
 });
+
+describe("edit tool stringified edits", () => {
+	it("parses edits from a JSON string", () => {
+		const definition = createEditToolDefinition(process.cwd());
+		const prepared = definition.prepareArguments!({
+			path: "file.txt",
+			edits: JSON.stringify([{ oldText: "a", newText: "b" }]),
+		});
+		expect(prepared).toEqual({
+			path: "file.txt",
+			edits: [{ oldText: "a", newText: "b" }],
+		});
+	});
+
+	it("leaves edits alone when the string is not valid JSON", () => {
+		const definition = createEditToolDefinition(process.cwd());
+		const prepared = definition.prepareArguments!({
+			path: "file.txt",
+			edits: "not json",
+		});
+		expect(prepared).toEqual({
+			path: "file.txt",
+			edits: "not json",
+		});
+	});
+});