From 5e86bc8eeb735b6afe39db4d741e51d33068b0ba Mon Sep 17 00:00:00 2001
From: kevin9327 <5299031+kevin9327@users.noreply.github.com>
Date: Sun, 13 Sep 2026 19:10:34 +0900
Subject: [PATCH] fix(runtime): write edit tool replacements literally

Without replace_all, the edit tool called String.prototype.replace with
new_string as the replacement string, so `$$`, `$&`, `` $` `` and `$'`
in new_string were expanded instead of written. An edit that inserts
`$$HOME` into a Makefile or a `$$` math block into Markdown wrote
different text than the model asked for. The replace_all path already
wrote new_string verbatim. Pass a replacer function so both paths agree.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
---
 packages/runtime/src/tools/built-in/fs.ts     |  3 ++-
 .../runtime/tests/tools/built-in/fs.test.ts   | 20 +++++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/packages/runtime/src/tools/built-in/fs.ts b/packages/runtime/src/tools/built-in/fs.ts
index 0025e05f..2ed212be 100644
--- a/packages/runtime/src/tools/built-in/fs.ts
+++ b/packages/runtime/src/tools/built-in/fs.ts
@@ -309,7 +309,8 @@ export async function edit(
   }
   const updated = replaceAll
     ? content.split(oldString).join(newString)
-    : content.replace(oldString, newString);
+    : // A replacer function keeps `$$`, `$&`, `` $` `` and `$'` literal.
+      content.replace(oldString, () => newString);
   await fs.writeFile(filePath, updated, "utf8");
   const totalReplaced = replaceAll ? occurrences : 1;
   return `Replaced ${totalReplaced} occurrence${totalReplaced === 1 ? "" : "s"} in ${filePath}`;
diff --git a/packages/runtime/tests/tools/built-in/fs.test.ts b/packages/runtime/tests/tools/built-in/fs.test.ts
index 05af89ad..df96b920 100644
--- a/packages/runtime/tests/tools/built-in/fs.test.ts
+++ b/packages/runtime/tests/tools/built-in/fs.test.ts
@@ -39,6 +39,26 @@ describe("filesystem built-in paths", () => {
     expect(await fs.readFile(absolutePath, "utf8")).toBe("after");
   });
 
+  test("edit writes $ sequences in new_string literally", async () => {
+    const directory = await fs.mkdtemp(
+      path.join(os.tmpdir(), "llm-space-fs-test-")
+    );
+    testDirectories.push(directory);
+    const newString = "echo $$HOME $& $' $`";
+    const allPath = path.join(directory, "all.mk");
+    const singlePath = path.join(directory, "single.mk");
+
+    await write(allPath, "run:\n\techo OLD\n");
+    await edit(allPath, "echo OLD", newString, true);
+    expect(await fs.readFile(allPath, "utf8")).toBe(`run:\n\t${newString}\n`);
+
+    await write(singlePath, "run:\n\techo OLD\n");
+    await edit(singlePath, "echo OLD", newString);
+    expect(await fs.readFile(singlePath, "utf8")).toBe(
+      `run:\n\t${newString}\n`
+    );
+  });
+
   test("write and edit expand a leading home shortcut", async () => {
     const directory = await fs.mkdtemp(
       path.join(os.homedir(), ".llm-space-fs-test-")