6. --schema on the jsonschema crate, offline, in every build

Status: accepted (2026-10-18), superseded in part by 0016 (2026-11-10)

Context

check-jsonschema reports no line numbers (its #359), and jsonvet already knows every value's offset, so it can put schema errors at their line and column.

Options

• Leave schemas to other tools.
• jsonschema with remote $ref and a SchemaStore catalog. Needs network access in hooks and CI, and a cache. Waits for a network policy.
• jsonschema offline, with each error's JSON Pointer mapped back to an offset.

Decision

Offline jsonschema, so every $ref stays inside the schema file, in every build since 3.0.0 (#54). A cargo feature first kept it out of the wheels, but nearly every install comes from PyPI: about 900 a week, against 11 crates.io downloads in total (2026-10-18).

Consequences

The x86-64 wheel grew from 0.67 to 4.33 MB, still under prek and ruff, and a plain check starts in 1.1 ms either way. About 70 more crates come along, one of them (num-cmp) unmaintained since 2017. A crafted schema can cost far more than its size, so --schema has limits, listed in design.md.

Confirmation

The limit tests in cli.rs's mod schema, and the packaging CI job, which builds the wheels.

Revisit if

Users ask for schemas picked by file name, jsonschema's Json trait settles so it can read our events directly, or the wheel size draws complaints.