Overview

Change-stream updateLookup and $_internalSearchIdLookup share the
SingleDocumentLookupExecutor / BatchedEnrichmentStage enrichment abstraction. This work extends
the per-engine lookup metrics to $_internalSearchIdLookup, adds per-consumer enrich-batch
counters, and broadens test coverage across the dimensions the shared module serves: _id shapes
(including fallback-handled declines), clustered collections, collation, sharding and placement
changes, concurrent DDL, batching knobs, and interrupts.

Observability

• Per-engine outcome and latency metrics for search idLookup under search.idLookup.sbe and
  search.idLookup.aggregation (found, notFound, notHandled, latencyMicros),
  wired in buildIdLookupExecutor().
• Per-consumer enrich-window counters changeStreams.updateLookup.enrichBatchesStarted and
  search.idLookup.enrichBatchesStarted, making batching knobs directly verifiable.

Test coverage

$_internalSearchIdLookup

• Coverage reworked around a shared mock-mongot util: _id shape matrix, unsupported shapes
  (regex/array) asserted to resolve cleanly through the fallback executor, mixed-shape batches
  with per-engine attribution, view-pipeline fallback, DDL between getMores, killOp mid-batch.
• Batching-knob invariance verified via the new enrich-batch counters.
• Sharding/DDL concurrency: shard-key strategy matrix, migration orphan filtering,
  parked-cursor-across-migration, view-backed orphan case.

Change-stream updateLookup

• Engine-attribution metrics tests across clustered/collation matrices, including mixed
  scalar/compound _id batches.
• Batching-knob verification with engine-based eligibility.
• DDL timing: update_lookup_before_ddl.js rework plus a new noPassthrough mid-batch file using
  the hangBeforeChangeStreamUpdateLookup fail point (mid-batch cached-acquisition staleness,
  killOp mid-batch).
• TooManyMatchingDocuments regression test for the sharded scatter-gather case.
• New shared helpers: expectedUpdateLookupEngine(), readUpdateLookupDelta(),
  assertChangeStreamEventsEqUnordered() / assertChangeStreamEventsEqWithDeploymentAwareness().

Unit tests

• SbeSingleDocumentLookupExecutor: decline paths for unsupported _id shapes (non-scalar _id
  support tracked as SERVER-134080), cached-plan survival across mid-sequence declines,
  accept-side allow-list, shard filtering, plan invalidation, lifecycle.
• Stats recorders: all factories plus cross-consumer cell independence, enrich-batch counters,
  and throw-integrity for the aggregation executor.

Observations recorded for follow-up

• The view-backed local-read executor appears not to request shard filtering (orphan returned);
  pinned as a KNOWN ISSUE assertion in the sharded DDL-concurrency test.
• The shard filter appears stale across a parked cursor even under SBE; pinned the same way.

Related

• SERVER-134017, SERVER-134080, SERVER-133661