Context

On non-primaries, verify delete oplog entries: before deleting, recompute the pre-image's hash and size and compare against the primary's m.h/m.sz. Deletes already have an apply-time sz verification in oplog.cpp (the delete path, gated mode == kSecondary).

No extra read is needed: the delete already fetches the pre-image (preImage) to remove it, and that is exactly the document we hash.

Generation and comparison happen together. On a mismatch, report through the same hook the sz check uses (log a repl constraint violation); the configurable off / log / crash behavior is
WS6.

Runs only on non-primaries (OplogApplication::Mode::kSecondary), with the feature flag on, for supported collections, and only when m.h is present.

Acceptance criteria

• Before deleting, the in-hand pre-image is hashed (SHA-256) and its size computed, then both compared against m.h/m.sz, beside the existing sz check.
• On mismatch, fassert and crash.
• Skipped on the primary, when the feature flag is off, on unsupported collections, and when m.h is absent.
• Inserts and updates are out of scope, and are filed as SERVER-128516 and [...]
• Unit-test