All five steps of the index-types review landed:
the refusal, the recorded corpus, partial indexes, hashed indexes, and
the implication test. `tests/spec/indexes/` is 48/48 and all four
recorded corpora are green -- positional 51, operators 125, indexes 48,
aggregate 70.
The review gets a fourth correction, and it is about method rather than a
fact. §4 asserted the implication rule without saying how to test it; the
answer needed no comparison of its own, because every operator the
partial-filter grammar admits is existential, so running the real matcher
against a stand-in document settles five operators at once.
What the review missed entirely was the gates. A corpus recorded from
mongod can see an implication test that says yes too readily -- documents
go missing -- but not one that never says yes, because no client can
observe which index a read used and this server has no `explain`. Both
numbers are recorded in PLAN §6 and the corpus README so the next change
to this code knows which gate is load-bearing for which direction.
Nothing else in M3 remains. PLAN §6 still carries the items this row
turned up and deliberately left: comparison operators are not
type-bracketed, a dotted path through an empty array reads as absent, a
key-pattern direction may be any non-zero number, three positional
divergences, three operator omissions, and the four older engine items.
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