Content-addressed result cache with dependency tracking for lanekeep.

A single-file, content-addressed store holding the violations, facts and tracked read dependencies of each file.

The cache is disposable by design: any read error means a cold recompute, never a failure. That is what makes a purpose-built on-disk format acceptable rather than reckless — nothing here can break a run, so the worst a format bug can do is cost time.

A hit needs two things

1. The key matches — same engine, same host API, same grammar, same ruleset, same config, same path, same bytes. See [key].
2. Every dependency still hashes the same — because ctx.readFile lets a result depend on files other than the one being checked. See [validate].

The second is what makes the first safe. Without it a rule that read package.json would keep its verdict after package.json changed, and nothing about the checked file would have changed to say otherwise.

The asymmetry that shapes everything here

Over-invalidating costs a recompute. Under-invalidating reports a stale answer and gives no sign it did — the output looks exactly like a correct one. So every doubtful input goes in the key, one damaged entry discards the whole file, and a dependency that cannot be hashed counts as changed.