10s delay under lefthook/pre-commit hooks — related to #524

[mAbduqayum]

Related to #524, but a different trigger.

#524 fixed the case where TERM=dumb caused a 10s hang. My TERM is normal (xterm-ghostty), but I still hit a 10s hang when treefmt runs from a git hook via lefthook.

What happens

Direct call: 23 ms. Same files via lefthook: 10 s. The 10s is reported by treefmt itself before any formatter runs.

$ time treefmt some.nix
formatted 0 files (0 changed) in 12ms        → 0.023s

$ time lefthook run pre-commit
formatted 0 files (0 changed) in 10.024s     → 10.044s

Why

Treefmt sends terminal color queries (OSC 10 / 11) on startup. Lefthook gives the child process a pty, so isTTY() returns true and the queries get sent — but there's no real terminal on the other end, so nothing answers. Treefmt waits the full OSC timeout (~10s).

#524's fix only short-circuits when TERM=dumb. With a normal TERM, we still run the probe and still hit the timeout.

Repro

lefthook.yml:

pre-commit:
  commands:
    format:
      glob: '*.nix'
      run: treefmt {staged_files}

treefmt.toml:

[formatter.nix]
command = 'nixfmt'
includes = ['*.nix']

Stage a .nix file, run lefthook run pre-commit.

Workarounds

• TERM=dumb in the hook env → 20 ms. Works.
• CI=1 → also works, but changes behaviour in other tools.
• NO_COLOR=1 → does not help. The probe still runs.

Versions

• treefmt v2.5.0
• lefthook v2.1.5
• NixOS, Linux 6.18