V8 12.0 snapshot version bump breaks embedder upgrades without rebuild

Compatibility boundary at isolate creation

V8 12.0 increments the internal snapshot version from 0x1108 to 0x1200, causing Isolate::CreateParams::snapshot_blob validation to reject blobs produced by V8 11.8's mksnapshot. Embedders that ship a prebuilt snapshot_blob.bin and dynamically link against a system V8 library see isolate creation fail with a "Snapshot version mismatch" error only after deployment, because local development typically builds the snapshot from the same source tree as the linked library.

Missing runtime negotiation

The V8 embedder documentation states snapshots are not forward-compatible and must be regenerated per major release, yet no version negotiation API or compatibility layer exists to detect the mismatch earlier or fall back to a no-snapshot isolate. Containerized deployments that mount a host libv8.so can silently diverge from the build-time version, delaying failure detection until the first isolate is created.

Is there a supported mechanism to query the expected snapshot version at embedder startup before isolate creation? Can an embedder safely fall back to a snapshot-less isolate when the version check fails, or does the API require the snapshot blob to be present and valid? What is the V8 project's current stance on introducing a compatibility shim or version negotiation for snapshot blobs across major releases?