Xcode's ACP client edit causes unwanted git activity #33502

Description

When adding an OpenCode ACP to Xcode as per their latest RC that adds ACP support (https://developer.apple.com/documentation/xcode-release-notes/xcode-26_6-release-notes), models using the edit tool result in Xcode staging the entire file that was touched. The chat window says "1 file created" even for an edit, so I suspect this is Xcode not understanding the edit tool's response correctly.

This feels like an Xcode problem, but I wonder if we can confirm that the edit tool's ACP messages are exactly to standard?

Xcode Agents chat

Findings
It seems that Xcode does this when it receives an ACP message with the following fields:

          "kind": "edit",
          "status": "completed",
          "locations": [
            {
              "path": "/Users/some/path/to/modified.file"
            }
          ],

When investigating this I noted that there is a specific clause in packages/opencode/src/tool/registry.ts that gives gpt-ish models apply_patch rather than edit, so this only occurs when using those specific models. apply_patch notably doesn't send the location for edits in the ACP payload. I ran a test ACP server and confirmed that it's the combination of "edit", "completed" and a valid location that causes this.

Plugins

none

OpenCode version

1.17.9

Steps to reproduce

1. Add opencode to Xcode 26.6 or higher as a custom ACP
2. Using a non-gpt model, ask for a file to be edited in the current project (specify not to use Xcode's MCP tools)
3. git status will show the file has been staged automatically regardless of Xcode's "automatically manage files" source control setting
4. Note that the same prompt from inside OpenCode directly does not stage anything as expected.

Screenshot and/or share link

No response

Operating System

macOS 26.5.1 (25F80)

Terminal

WezTerm