E2BIG: argument list too long, posix_spawn 'git' on revert in large repos (~19K files) #22533

Description

When attempting to revert a message in a session running in a large repository (~19K tracked files), the revert operation fails with:

E2BIG: argument list too long, posix_spawn 'git'

The error is reproducible — every revert attempt in this project fails.

Environment

• opencode version: 1.4.4
• OS: Arch Linux 6.19.11 (x86_64)
• ARG_MAX: 2,097,152 bytes (2 MB)
• Repo size: 19,111 tracked git files, average path length ~103 bytes (~2 MB total path data)

Reproduction

1. Open a session in a git repo with ~19K+ tracked files
2. Send a message to the agent
3. Attempt to revert the message

Logs

ERROR 2026-04-15T02:30:59 +88ms service=server error=E2BIG: argument list too long, posix_spawn 'git' failed

From ~/.local/share/opencode/log/:

service=server method=POST path=/session/<id>/revert request
service=server messageID=<id> revert
ERROR service=server error=E2BIG: argument list too long, posix_spawn 'git' failed

Root Cause

In packages/opencode/src/snapshot/index.ts, the add(), patch(), and diffFull() functions pass all changed/untracked file paths as command-line arguments to git check-ignore:

const checkArgs = [
  ...quote,
  "--git-dir", path.join(state.worktree, ".git"),
  "--work-tree", state.worktree,
  "check-ignore", "--no-index",
  "--", ...all,  // <-- ALL files as CLI args
]
const check = yield* git(checkArgs, { cwd: state.directory })

During a revert, the snapshot index diverges from the working tree, causing diff-files and ls-files --others to return a large number of files. With ~19K files × ~103 bytes average path + config flags + env vars, the total argument size exceeds the Linux ARG_MAX limit of 2 MB.

The same pattern also appears in:

• patch() — check-ignore --no-index -- ...files
• diffFull() — check-ignore --no-index -- ...files
• add() — git rm --cached -f -- ...ignoredFiles

Suggested Fix

Replace CLI argument passing with stdin-based communication for git check-ignore:

// Instead of:
git(["check-ignore", "--no-index", "--", ...files])

// Use stdin (-z for null-separated, --stdin for reading from stdin):
git(["check-ignore", "--no-index", "--stdin", "-z"], { stdin: files.join("\0") })

This avoids the OS argument length limit entirely. The same pattern should be applied to git rm --cached calls (using --stdin or xargs-style batching).

Alternatively, the file list could be batched into chunks that stay well under ARG_MAX.