chore(spec): retire IDataEngine.batch? per ADR-0119 D3 — declared-but-unimplemented, zero callers #4618

ADR-0119 D3 rules IDataEngine.batch? retired. This issue is the mechanical removal.

ADR renumbered. This issue originally cited ADR-0118. That record is now ADR-0119 (docs/adr/0119-plugin-reachable-transactions-and-honest-atomic-batch.md) — it merged the same day as an unrelated ADR-0118 (非用户 actor 的平台契约), and the earlier merge holds the number.

The finding

packages/spec/src/contracts/data-engine.ts:97-100:

/**
 * Batch Operations (Transactional)
 */
batch?(requests: DataEngineRequest[], options?: { transaction?: boolean }): Promise;

• No engine implements it. ObjectQL has no batch method; there is no other engine in the tree.
• No caller invokes it. DataEngineRequest is imported by exactly one non-spec file — the contract declaring it.
• The doc comment is three words, specifying nothing about partial failure, ordering, cross-object refs, rollback scope, or what transaction: false means. Contrast the deliberate, evidenced optionality of its neighbours getDefaultDriverName?/getDriverByName? (:107-118), which name their implementer and their probing caller.
• Its DataEngineRequestSchema union (packages/spec/src/data/data-engine.zod.ts:706-717) even nests batch requests recursively — a shape nobody designed against because nobody built it.
• The only "test" is packages/spec/src/contracts/data-engine.test.ts:162-177, which builds an ad-hoc object literal with a batch property and asserts it is defined. It pins the type, not an implementation.

A declared capability that cannot be exercised is precisely ADR-0049's enforce-or-remove target. ADR-0119 D1 (transaction on IObjectQLEngine) and D4 (real atomic batchData) now cover its stated purpose in-process, and POST {basePath}/batch covers it on the wire.

Work

Follow the spec-property-retirement playbook, contract-member route — this is a TypeScript contract member, not an authorable Zod metadata key, so there is no retiredKey tombstone to add (nothing can "author" it; the removal is invisible to metadata authors and visible only to TS consumers).

1. Delete the member at data-engine.ts:97-100; drop the type-only test case at data-engine.test.ts:162-177.
2. Decide DataEngineRequest / DataEngineBatchRequestSchema's fate (data-engine.zod.ts:694-717, 764) — if the union has no other live reader after the member goes, it retires with it; if the wire-side batch still uses part of it, keep exactly that part and say so.
3. Rebuild spec before running the generated-artifact check (pnpm --filter @objectstack/spec build && pnpm --filter @objectstack/spec check:generated) — check:api-surface reads dist, and a stale dist produces a phantom-removal diff.
4. Changeset carrying the FROM → TO migration text, since it ships to consumers as the package CHANGELOG: "IDataEngine.batch? is removed. It was never implemented by any engine and had no callers. For in-process multi-write atomicity use IObjectQLEngine.transaction(cb); for a batch over one object use the metadata protocol's batchData with options.atomic: true; on the wire use POST {basePath}/batch."
5. Upgrade-guide entry per ADR-0087's removal discipline.

Refs: ADR-0119 D3, ADR-0049, #4612.