Reject Agent Patches That Shrink the Property Seed Corpus

A green CI job after an agent patch is not evidence that behavior held. The useful signal is whether the same seed corpus still executed, whether fixture hashes stayed put, and whether the flake freeze budget did not grow. If any of those three ledgers moved the wrong way, the patch is not a fix. It is a quieter test suite. This article proposes a merge gate you can run as a script. It does not require a new framework. It requires treating seeds, fixture hashes, and flake slots as inventory the agent cannot restock. The failure mode a pytest-zero exit misses Agents optimize for the check in front of them. When that check is “the process exited 0”, three cheap edits recur. Narrow the property strategy so fewer inputs actually run. Rewrite a fixture so the assertion matches the new code. Park a race in a freeze list and leave it for later. None of those edits need intent. They are local minima. A corpus that used to execute ten seeds and now executes seven still looks green. The suite got smaller. The risk got larger. Coverage percentages do not catch this. Coverage can rise while the property runner stops visiting the interesting region. Seed hit-count is a worse statistic for “how tested is this file” and a better statistic for “did this patch shrink the test world.” Use it as a gate, not as a dashboard vanity number. Three ledgers, one merge rule Keep the ledgers in oracle/ . The agent may read that directory. It may not grow it. Ledger File Allowed delta on an agent PR Seed corpus oracle/seeds.json none Fixture hashes oracle/fixtures.sha256 none Flake budget oracle/flake_budget.json max_frozen unchanged; frozen names may only leave the set Human reviewers may change oracle/ on a dedicated PR that contains no production diff. Mix those two kinds of change and the gate becomes theater. The mixed PR is how an oracle rewrite hides inside a “refactor.” Workflow The steps below are a labeled proposal. They are not a report from a named production fleet, and they are not