Write Gitlink-approved file content byte-for-byte (no newline translation)

[dovvnloading]

Summary

apply_change_set wrote approved file content with write_text's default newline handling, which translates on write: on Windows \n becomes \r\n and an existing \r\n becomes \r\r\n. So the file that lands on disk diverges from exactly what the user approved — and the approval preview diffs via splitlines() (line-ending-agnostic), so the drift was invisible.

Demonstrated on Windows: approved b"a\nb\r\nc\n" was written as b"a\r\nb\r\r\nc\r\n" (note the doubled \r\r\n). Tellingly, the rollback path one block down already restored byte-exact via write_bytes — so a restore was more faithful than the original apply.

Fix

Pass newline="" to write_text so the approved content is written exactly, byte-for-byte. One line; the rest is a comment and tests.

Test plan

• Regression tests assert the on-disk bytes — read_text() would mask this by translating newlines back on read, so they use read_bytes(): a mixed \n/\r\n payload round-trips exactly and never contains \r\r\n; an LF-only update stays LF.
• Full suite: 1694 passed, zero regressions
• Confirmed on Windows that the pre-fix code produced the CR-CR-LF corruption and the fix writes byte-exact

Second of the fixes from the recent adversarial bug-scan (after #91).