Crate lattice_format 

External formatters, and how their output reaches a buffer.

The external-tool half of auto-indent (docs/dev/architecture/auto-indent.md §8). Where the indent engine answers “which column does this line start at” synchronously from a parse tree, this runs somebody else’s program and turns its opinion into edits.

Three concerns, three modules, because they fail differently:

• spec — which program, per language. Data.
• runner — spawning it, with a timeout and a typed error per failure mode. Blocking; the caller puts it on spawn_blocking.
• apply — whole-file output → a minimal edit set, never a buffer-wide replace.

Why this is a crate and the indent engine is not

lattice-indent was proposed, built and collapsed into lattice-syntax during IN.1: a pure tree walk driven by .scm files belongs beside the other tree walks. This is genuinely different work — process spawning, a timeout policy, stderr handling, diff-based edit derivation — and none of it belongs in a syntax crate.

Re-exports

pub use apply::changes_more_than_indentation;

pub use apply::minimal_edits;

pub use runner::FORMAT_TIMEOUT;

pub use runner::FormatError;

pub use runner::run;

pub use spec::FormatterSpec;

Modules

apply

Turning a formatter’s whole-file output into a minimal edit set.

runner

Running a formatter, with the failure modes spelled out.

spec

What to run, per language.