Doug Richardson 91a1faedcc Add PREK_MAX_CONCURRENCY environment variable (#1697) ...

## Summary

- Add `PREK_MAX_CONCURRENCY` environment variable to cap the maximum
number of concurrent hooks
- Value is floored at 1; values above CPU count are allowed (useful for
I/O-bound hooks)
- Invalid values show a user-visible warning and fall back to CPU count
- `PREK_NO_CONCURRENCY` takes precedence when both are set

## Motivation

When `ulimit -n` is low, concurrent hook execution can exhaust file
descriptors. This provides an environment variable to limit concurrency.

For #1696

## Test plan

- [x] `mise run lint` — no warnings
- [x] `mise run test` — all tests pass
- [x] Unit tests for `resolve_concurrency`: valid value, above CPU
count, zero floors to 1, invalid string, empty string, unset,
no_concurrency, no_concurrency overrides max

Co-authored-by: Claude <noreply@anthropic.com>

2026-02-27 12:01:53 +08:00

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proposals

Add mdformat pre-commit hook (#1416)

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authoring-hooks.md

Add install source detection for mise (#1605)

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benchmark.md

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builtin.md

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changelog.md

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cli.md

Add prek util list-builtins command (#1600)

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configuration.md

Add PREK_MAX_CONCURRENCY environment variable (#1697)

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debugging.md

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diff.md

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faq.md

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index.md

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installation.md

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integrations.md

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languages.md

Use --locked for Rust cargo install commands (#1661)

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quickstart.md

Update quick start to use prek.toml (#1576)

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requirements.in

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requirements.txt

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workspace.md

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