Rename use_legacy_parsers → use_new_parsers with clearer semantics
The flag now has intuitive semantics:
- use_new_parsers=false (default): Use legacy monolithic parsers
- use_new_parsers=true: Use new modular PEG parsers
Also adds LLAMA_USE_NEW_PARSERS env var to enable new parsers in tests,
and ensures needle streaming tests explicitly use new parsers.
This makes the "safe default" truly safe - no behavior change by default.
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>