test(metadata-protocol): re-measure the deleted-datasource prolongation across replicas after #13331's fix (#14431)

* test(metadata-protocol): re-verify deleted-datasource prolongation across replicas

WIP — measurement harness for #13609: two protocol replicas over one shared
sys_metadata store, measuring how long the peer's /api/v1/meta/datasource read
door keeps serving a deleted datasource, with and without the landed #13331
publisher + cluster bridge.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0112hMx9hjJ9BgB28X97DS68

* test(metadata-protocol): measure deleted-datasource prolongation across replicas

Re-verification for #13609, the carrier the maintainer's ruling left open for
it: with #13331's publisher + service-cluster bridge landed, how long does a
peer replica keep serving a deleted datasource on the /api/v1/meta/datasource
read door?

Two protocol replicas over one shared sys_metadata store, each with its own
registry, overlay cache and write epoch, joined by a real cross-instance
transport. Declared as a PROXY for a live multi-node deployment, which is not
reachable from this container.

Measured: the bridge does heal the peer's registry within one bus hop, but the
peer's overlay cache is not invalidated by the convergence, and any read of the
peer's own door inside that residue window re-hydrates the deleted row back
into the untimed registry. So the prolongation is bounded by one 30s TTL window
only when no read lands in the window, and unbounded when one does.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0112hMx9hjJ9BgB28X97DS68

* chore: record the new measurement file's engine doubles in the pinned ledger

Gate scaffolding for check:engine-double-contract, produced by
`node scripts/check-engine-double-contract.mjs --write`. The three rows are the
delete/findOne/update doubles of the #13609 measurement harness, all already
routed through assertEngine*Dispatch; the ledger just has to learn about the
file or it never protects it.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0112hMx9hjJ9BgB28X97DS68

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Co-authored-by: Claude <noreply@anthropic.com>

Author: os-musk