Motivation
Large test suites should be distributable across multiple CI workers without maintaining separate file lists.
Proposed work
- Add shard index and total shard count options.
- Use a deterministic assignment based on normalized test identity.
- Support file-level sharding initially and document whether test-level sharding is possible.
- Print shard selection and totals in summaries.
- Combine cleanly with filtering, random seeds, retries, and coverage.
Acceptance criteria
- The union of all shards contains every selected test exactly once.
- The same inputs always produce the same shard assignment.
- Invalid shard parameters fail with clear messages.
- CI documentation includes a matrix example.