ADR-0005: Capability-declared adapters, never emulate

• Status: Accepted
• Related: ST-009, PRD §7.3, §12.5, §27.5

Context #

Runners and VCS providers differ. Some support test-case selection, per-test coverage, rename detection or merge-base, and some don't. Quietly approximating a missing feature would weaken selection safety without anyone noticing.

Decision #

• Every adapter returns a capabilities object where each value is true | false | "partial". Anything not declared counts as unsupported.
• The impact engine adapts its granularity to what the adapter declares. For example, it selects at file level when test-case selection is unsupported. Any downgrade is reported in the decision's warnings.
• A conformance kit in plugin-sdk checks the declared capabilities against fixtures.

Consequences #

• Selection may be coarser on some runners. That is fine because it stays honest.
• Third-party adapters get a clear contract and a test suite to run against.

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