Add DAG-based hook scheduling with group and after

[drichardson]

Summary

• Adds two new optional config fields — group and after — that let users express a DAG of hook dependencies
• prek builds the DAG, schedules maximally parallel execution, and only serializes where explicit dependency edges exist
• priority continues to work unchanged; priority and group/after are mutually exclusive on the same hook
• Includes cycle detection, unknown reference errors, and 7 new integration tests
• See docs/proposals/dag-scheduling.md for the full design

Test plan

• cargo build compiles
• All 294 existing unit tests pass
• All 59 existing integration tests pass (1 pre-existing failure in run_in_non_git_repo unrelated to this change)
• 7 new DAG scheduling integration tests pass
• Priority-based tests (priority_fail_fast_stops_later_groups, priority_group_modified_files_is_group_failure_and_output_is_indented) pass unchanged
• JSON schema regenerated with new fields
• cargo clippy and cargo fmt clean

🤖 Assisted by Claude Code

[drichardson]

oops, didn't mean to request a review on this yet

[codecov]

Codecov Report

❌ Patch coverage is 95.94595% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.62%. Comparing base (e290094) to head (a713507).
⚠️ Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
crates/prek/src/cli/run/run.rs	95.87%	9 Missing ⚠️
crates/prek/src/hook.rs	94.28%	2 Missing ⚠️
crates/prek/src/config.rs	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1704      +/-   ##
==========================================
+ Coverage   91.43%   91.62%   +0.18%     
==========================================
  Files          96       96              
  Lines       18892    19235     +343     
==========================================
+ Hits        17274    17624     +350     
+ Misses       1618     1611       -7     

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[prek-ci-bot]

📦 Cargo Bloat Comparison

Binary size change: +0.00% (23.9 MiB → 23.9 MiB)

Expand for cargo-bloat output

Head Branch Results

 File  .text    Size             Crate Name
 0.3%   0.8% 79.5KiB             prek? <prek::cli::Command as clap_builder::derive::Subcommand>::augment_subcommands
 0.3%   0.7% 73.8KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.3%   0.7% 71.1KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.2%   0.5% 51.2KiB annotate_snippets annotate_snippets::renderer::render::render
 0.2%   0.5% 50.5KiB              prek prek::languages::<impl prek::config::Language>::install::{{closure}}
 0.2%   0.4% 40.0KiB              prek prek::cli::run::run::run::{{closure}}
 0.2%   0.4% 39.1KiB              prek prek::run::{{closure}}
 0.1%   0.3% 31.3KiB             prek? <prek::cli::RunArgs as clap_builder::derive::Args>::augment_args
 0.1%   0.3% 28.5KiB      serde_saphyr saphyr_parser_bw::scanner::Scanner<T>::fetch_more_tokens
 0.1%   0.2% 24.7KiB             prek? <prek::config::_::<impl serde_core::de::Deserialize for prek::config::Config>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map
 0.1%   0.2% 22.8KiB      serde_saphyr saphyr_parser_bw::scanner::Scanner<T>::fetch_more_tokens
 0.1%   0.2% 22.7KiB              prek <prek::languages::ruby::ruby::Ruby as prek::languages::LanguageImpl>::install::{{closure}}
 0.1%   0.2% 21.5KiB              prek prek::hooks::meta_hooks::MetaHooks::run::{{closure}}
 0.1%   0.2% 21.1KiB      clap_builder clap_builder::parser::parser::Parser::get_matches_with
 0.1%   0.2% 20.3KiB     serde_saphyr? <serde_saphyr::de::YamlDeserializer as serde_core::de::Deserializer>::deserialize_map
 0.1%   0.2% 20.2KiB               std core::ptr::drop_in_place<prek::languages::<impl prek::config::Language>::install::{{closure}}>
 0.1%   0.2% 20.0KiB   cargo_metadata? <cargo_metadata::_::<impl serde_core::de::Deserialize for cargo_metadata::Package>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map
 0.1%   0.2% 19.6KiB              prek prek::archive::unzip::{{closure}}
 0.1%   0.2% 18.6KiB              ring ring_core_0_17_14__x25519_ge_frombytes_vartime
 0.1%   0.2% 18.5KiB              prek prek::cli::run::filter::collect_files_from_args::{{closure}}
38.4%  91.7%  9.2MiB                   And 21151 smaller methods. Use -n N to show more.
41.8% 100.0% 10.0MiB                   .text section size, the file size is 23.9MiB

Base Branch Results

 File  .text    Size             Crate Name
 0.3%   0.7% 71.4KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.3%   0.7% 70.6KiB             prek? <prek::cli::Command as clap_builder::derive::Subcommand>::augment_subcommands
 0.3%   0.6% 65.6KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.2%   0.5% 51.2KiB annotate_snippets annotate_snippets::renderer::render::render
 0.2%   0.5% 50.5KiB              prek prek::languages::<impl prek::config::Language>::install::{{closure}}
 0.2%   0.4% 41.5KiB              prek prek::cli::run::run::run::{{closure}}
 0.2%   0.4% 38.8KiB              prek prek::run::{{closure}}
 0.1%   0.3% 32.0KiB             prek? <prek::cli::RunArgs as clap_builder::derive::Args>::augment_args
 0.1%   0.3% 28.5KiB      serde_saphyr saphyr_parser_bw::scanner::Scanner<T>::fetch_more_tokens
 0.1%   0.2% 24.7KiB             prek? <prek::config::_::<impl serde_core::de::Deserialize for prek::config::Config>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map
 0.1%   0.2% 22.8KiB      serde_saphyr saphyr_parser_bw::scanner::Scanner<T>::fetch_more_tokens
 0.1%   0.2% 22.7KiB              prek <prek::languages::ruby::ruby::Ruby as prek::languages::LanguageImpl>::install::{{closure}}
 0.1%   0.2% 22.5KiB              prek prek::hooks::meta_hooks::MetaHooks::run::{{closure}}
 0.1%   0.2% 21.1KiB      clap_builder clap_builder::parser::parser::Parser::get_matches_with
 0.1%   0.2% 20.8KiB              prek prek::hooks::meta_hooks::MetaHooks::run::{{closure}}
 0.1%   0.2% 20.2KiB               std core::ptr::drop_in_place<prek::languages::<impl prek::config::Language>::install::{{closure}}>
 0.1%   0.2% 19.4KiB   cargo_metadata? <cargo_metadata::_::<impl serde_core::de::Deserialize for cargo_metadata::Package>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map
 0.1%   0.2% 19.2KiB              prek prek::archive::unzip::{{closure}}
 0.1%   0.2% 18.7KiB     serde_saphyr? <serde_saphyr::de::YamlDeserializer as serde_core::de::Deserializer>::deserialize_map
 0.1%   0.2% 18.6KiB     serde_saphyr? <serde_saphyr::de::YamlDeserializer as serde_core::de::Deserializer>::deserialize_map
38.3%  91.8%  9.2MiB                   And 21074 smaller methods. Use -n N to show more.
41.8% 100.0% 10.0MiB                   .text section size, the file size is 23.9MiB