Windows 1.2.20: Agent edits stop showing Modified Files and /undo does not restore files #16391

Description

On Windows in 1.2.20, when Agent edits files in a Git repository, the TUI no longer shows Modified Files, and /undo only rewinds the conversation state while leaving the edited files unchanged.

This worked in 1.2.19. I also confirmed locally that reverting commit 74effa8eec01b3cb816178a37921333420fe2d82 on top of 1.2.20 restores the previous behavior.

OpenCode version

1.2.20

Steps to reproduce

1. On Windows PowerShell, open a Git repository with OpenCode 1.2.20.
2. Ask the Agent to modify a file.
3. Observe that the TUI sidebar does not show Modified Files.
4. Run /undo.
5. Observe that the conversation rewinds, but the edited file is not restored.

Expected behavior

Agent edits should appear under Modified Files, and /undo should restore the file changes from the last step.

Actual behavior

The sidebar shows no Modified Files, and /undo only rewinds the conversation state.

Screenshot and/or share link

N/A

Operating System

Windows 11

Terminal

PowerShell 7

console.log({
  PATH: process.env.PATH ?? null,
  Path: process.env.Path ?? null,
  which_git: which("git"),
  bun_git: Bun.which("git") ?? null,
  git: await Process.run(["git", "--version"], { nothrow: true }),
})

{
  "PATH": null,
  "Path": "...;C:\\Program Files\\Git\\cmd;...",
  "which_git": null,
  "bun_git": "C:\\Program Files\\Git\\cmd\\git.exe",
  "git": {
    "code": 0,
    "stdout": "git version 2.53.0.windows.1\n"
  }
}

Note: this issue text was generated by GPT 5.4 and reviewed against a local repro.