apply_patch: parallel calls on the same file silently drop one change

[hooop]

Description

When a model sends two apply_patch calls for the same file in one response, both calls can read the original file. Both report success, but the last write overwrites the first change.

I reproduced this with GPT-6.1 Sol and "permission": { "edit": "ask" }: both approval prompts showed the original file, I approved both, and only the second change was kept.

The edit tool already serializes same-file edits with a per-file lock (#23483), but apply_patch does not. Related but different: #31776 and PR #47956 concern a file changed outside OpenCode during approval.

Plugins

None

OpenCode version

1.18.34

Steps to reproduce

1. Create settings.txt with:

   top = 0
   middle = keep
   bottom = 0
   

2. Create opencode.json with:

   {
     "$schema": "https://opencode.ai/config.json",
     "permission": {
       "edit": "ask"
     }
   }

3. Start OpenCode 1.18.34 and select GPT-6.1 Sol.

4. Send this prompt:

   In settings.txt, change top = 0 to top = 1 and bottom = 0 to bottom = 2. Use two separate apply_patch calls, sent in parallel in the same response.
   

5. Confirm that both apply_patch calls appear in the same assistant response and that both approval requests show the original file.

6. Approve both requests.

Expected result

top = 1
middle = keep
bottom = 2

Actual result

Both calls report success, but the final file contains:

top = 0
middle = keep
bottom = 2

Screenshot and/or share link

No response

Operating System

macOS 26.3

Terminal

Terminal.app

[github-actions]

---

This issue might be a duplicate of an existing issue. Please check:

• apply_patch silently drops earlier duplicate Update File operations #48474: apply_patch silently drops earlier changes when multiple Update File sections target the same file in one call, due to each update being based on the original file contents.

[hooop]

Thanks for flagging #48474. I checked it, but this is a different concurrency case.

#48474 uses a single apply_patch call containing multiple *** Update File sections for the same path. In this issue, there are two independent apply_patch tool calls sent in parallel, and each call contains only one update for the file.

The calls can both read the same original content before either writes, so the last complete-file write overwrites the other call’s change. Fixing multiple sections within one invocation would not serialize these separate concurrent calls, and a per-file lock between calls would not fix #48474’s single-call behavior.

[neriousy]

Fixed on v2, here's how to upgrade: https://opencode.ai/v2/docs