Folded from PR #98345 (@ericmaddox): the one scenario its suite covered
that #91557's did not — an assistant message between the image-only user
message and the checkpoint, asserting post-prune ordering.
Preserve valid normalized input_image user messages across native-compaction checkpoints at bounded one-token retention cost. Keep text extraction text-only, reject malformed or unknown multipart placeholders, and prove the production adapter path without claiming unsupported input_file behavior.
Republish the identical source tree after an unrelated nondeterministic focus-redraw test failure; this commit contains no source delta from the previously verified object.
Refs #90976 and #91477.
Eric Maddox