Two primitives¶

A harness.yaml is mostly slots and rules. Other objects preserve execution facts without expanding the author model.

Slot¶

A Slot gives an artifact a stable name, kind, and materialization path.

slots:
  brief: { kind: file, path: request/brief.md }
  candidate: { kind: git, path: artifacts/candidate }
  report: { kind: file, path: artifacts/report.md }

Each committed version in a Slot is an immutable Revision. The kernel can therefore identify exactly what a Rule read and decide whether an existing output still matches the current inputs.

Rule¶

A Rule declares its inputs, outputs, and execution method.

rules:
  - id: write_report
    in: [brief, candidate]
    out: [report]
    run: "printf '# Report\n' > out/report"

At execution time, inputs appear under in/ and declared outputs must be written under out/. A successful Attempt commits every output atomically. Failure, timeout, or a missing output leaves no partial Revision.

Runtime facts¶

Name	Meaning
Revision	An immutable artifact version in a Slot
Activation	A Rule paired with an exact input Revision frontier
Attempt	One execution of an Activation
Receipt	The reusable record of a successful execution

A Lease prevents multiple workers from owning the same Activation. A Session lets an executor retain controlled context across related runs. Both are runtime mechanisms.

Three common execution methods¶

A Shell Rule runs a command. An Agent Rule delegates semantic work to an executor. A Human Rule pauses for a responsible decision.

run: "cp in/source out/result"

run:
  using: codex
  command: "Read in/brief and write only out/report."

run:
  using: human
  command: "Approve the reviewed candidate"

All three share Slot and Rule dataflow, so they compose in the same graph.