The .env sanitizer inferred missing newlines from known KEY= substrings
inside existing values. Plain secrets containing those bytes could therefore
be split into synthetic assignments and rewritten to disk.
Treat each physical line as the only assignment boundary and keep bytes after
the first equals sign opaque for boundary discovery. Preserve safe formatting,
null-byte removal, BOM handling, and normal one-assignment-per-line parsing.
Cover direct loading, dotenv loading, sanitization, writers, and migration
with behavioral regressions.
Fixes#29155
- Move test file to tests/hermes_cli/ (consistent with test layout)
- Remove unused imports (os, pytest) from test file
- Update _sanitize_env_lines docstring: now used on read + write paths