CDict initialization already routes content copying and dictionary insertion
through the Rust orchestrator, but its private C adapter still hard-coded the
full table-load method and the CDict table-fill purpose. That split left an
important advanced-CDict content-loading policy hidden in the C bridge and
made the callback contract less explicit.
Extend the private insertion callback with the two table-loading policy
values. Rust now selects the full-load and for-CDict modes after its content
branch and before invoking the opaque C operation. C retains only the private
CDict layout projection and forwards those selected values to the existing
content loader, preserving the original insertion order and behavior.
The focused initialization probes record both values in the callback and
assert them for by-reference and by-copy dictionaries alongside the existing
ordering and content-copy checks.
Test Plan:
- `rustfmt +nightly --edition 2021 --check rust/src/zstd_compress_dictionary.rs` -- passed
- `ulimit -v 41943040; gcc -fsyntax-only -std=c99 -DXXH_NAMESPACE=ZSTD_ -DDEBUGLEVEL=0 -DZSTD_MULTITHREAD -DZSTD_LEGACY_SUPPORT=5 -Ilib -Ilib/common -Ilib/compress -Ilib/decompress -Ilib/dict -Ilib/deprecated lib/compress/zstd_compress.c` -- passed
- `ulimit -v 41943040; clang -fsyntax-only -std=c99 -DXXH_NAMESPACE=ZSTD_ -DDEBUGLEVEL=0 -DZSTD_MULTITHREAD -DZSTD_LEGACY_SUPPORT=5 -DZSTD_NO_ASM=1 -Ilib -Ilib/common -Ilib/compress -Ilib/decompress -Ilib/dict -Ilib/deprecated lib/compress/zstd_compress.c` -- passed
- `git diff --check` and `git diff --cached --check` -- passed
- Cargo, make, native builds, fuzzers, and large tests were not run per task constraints
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