## Summary
- Fixed buffer overflow in env_loader when parsing large environment
variables with escape sequences
- Replaced fixed 4096-byte buffer with a stack fallback allocator that
automatically switches to heap allocation for larger values
- Added comprehensive tests to prevent regression
## Background
The env_loader previously used a fixed threadlocal buffer that could
overflow when parsing environment variables containing escape sequences.
This caused crashes when the parsed value exceeded 4KB.
## Changes
- Replaced fixed buffer with `StackFallbackAllocator` that uses 4KB
stack buffer for common cases and falls back to heap for larger values
- Updated all env parsing functions to accept a reusable buffer
parameter
- Added proper memory cleanup with defer statements
## Test plan
- [x] Added test cases for large environment variables with escape
sequences
- [x] Added test for values larger than 4KB
- [x] Added edge case tests (empty quotes, escape at EOF)
- [x] All existing env tests continue to pass
fixes#11627
fixes BAPI-1274
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Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
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