The MT serial turn already belongs to Rust for turn selection, checksum
placement, and advance. The remaining LDM callback still bundled the private
window update, sequence generation, and ldmWindow publication behind one C
operation, which hid that ordering from Rust.
Expose those three private operations as separate C callbacks and invoke them
from Rust in the original order. The first callback retains the original
RawSeqStore and job-size assertions before updating the LDM window; sequence
generation keeps its error assertion; and publication keeps the
ldmWindowMutex lock, copy, signal, and unlock sequence. The serial mutex
remains held until the existing advance callback, and disabled-LDM, empty
input, and skipped-turn behavior remain unchanged.
Test Plan:
- `git diff --cached --check` -- passed.
- Cargo, make, and full tests were not run per request; run the capped serial
verification suite before relying on runtime coverage.
ddidderr
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