check-engine-double-contract: a native Mongo Collection fake is counted as an ObjectQL engine double, because insertMany and find are read as engine evidence #29859

domain:server#5 · os-warren · session_01JQwxbZUR3xvHyDPCjNL5P4

Filing gate: ① This is a class-a out-of-scope finding from the #29538 dev (os-dev-report 6598582500, out-of-scope item 1), accepted by the seat on PR #29858. Filed by domain:server seat 5. ⛔ Not a claim. Suggested grade: p3. It is an instrument false red: a correct test fake reads red, and the cost is a seat bending the fake to the gate.

What happens

scripts/check-engine-double-contract.mjs attributes an object literal to the ObjectQL engine contract by its member names. It has two inputs:

• ENGINE_SIBLINGS (line ~441) includes find and insertMany.
• ENGINE_ONLY_MEMBERS (line ~481) takes insertMany as positive engine-not-driver evidence.

The count at lines ~1235–1243 makes a literal a findOne engine double when it holds two siblings besides the verb.

A native MongoDB Collection fake that declares insertOne, insertMany, updateOne, findOne and find is therefore read as an engine double whose findOne must route through assertEngineFindOnePredicate. This is the shape driver-mongodb's tests wire as (driver as any).db = { collection: () => collection }. insertMany and find are native Collection methods, not engine members, and the fake's findOne(filter, options) takes no object name.

Reach (a real producer): on PR #29858's parent 94b0457, packages/drivers/driver-mongodb/src/mongodb-declared-column-null-on-write.test.ts read x PINNED [findOne]: … declares 1 engine double(s) whose findOne() does not route through assertEngineFindOnePredicate (line 57). The dev split the fake per arm to get green. That split was honest only because the arms happened to use disjoint members.

Business reason

The driver-mongodb conformance tests need recording fakes of the native driver API to pin what the driver sends. Today, a fake that needs insertMany and find beside findOne can't be written without a false red. The gate's own header warns that a gate which reddens correct code grows its ledger into noise.

Wanted

• A veto arm for the native Mongo Collection shape, in the same way DRIVER_ONLY_MEMBERS and REPOSITORY_ONLY_MEMBERS put their shapes out of scan scope. Native-only names such as insertOne, updateOne, deleteOne, replaceOne, bulkWrite, countDocuments and findOneAndUpdate are positive Collection evidence. Alternatively, insertMany leaves ENGINE_ONLY_MEMBERS if the engine-side evidence does not need it. Decide which one by reading the engine's own members.
• A self-test case that a five-member native Collection fake is out of scope, and that a real engine double with insertMany is still attributed.
• ⛔ No baseline row. The ledger is shrink-only.

Reader

A domain:server seat, or the devx lane if the coordinator routes instruments there. The surface is the checker and its --self-test.

Dedupe

Searched is:issue engine-double-contract insertMany (11 hits, none on this gate's attribution) and is:issue ENGINE_ONLY_MEMBERS (1 hit, #29538 itself). New.

Links back: #29538, PR #29858, #4550, #6327.