docs(rewrite): commit intentional deviations as fix-deviant(...) and register them

docs/rewrite/AGENT_GUIDE.md

@@ -15,10 +15,14 @@ You are porting part of Ghostty 1.3.1 (Zig) to Rust. Read
    own crate's `Cargo.toml` (prefer well-known crates; use `cargo add -p <crate>`).
 2. **Faithful port — except genuine bugs.** If the Zig code has a real
    memory-safety bug or undefined behaviour (use-after-free, out-of-bounds,
-   leaks, stale pointers, infinite loops, integer overflow UB), do NOT
-   replicate it: implement the evidently intended, safe behaviour, add a test,
-   and record it under "Upstream bugs fixed" in your notes (Zig file:line,
-   what was wrong, what the Rust does). Everything else stays faithful.
+   leaks, stale pointers, infinite loops, integer overflow UB) or a clear
+   data-loss/corruption bug (lost or overwritten output), do NOT replicate
+   it: implement the evidently intended, safe behaviour, add a test, record
+   it under "Upstream bugs fixed" in your notes (Zig file:line, what was
+   wrong, what the Rust does) and add an entry to docs/rewrite/DEVIANT_FIXES.md.
+   Keep each such fix in separate hunks/files where possible: the
+   orchestrator commits every deviant fix on its own, titled
+   `fix-deviant(<scope>): ...`. Everything else stays faithful.
    Original rule 2:
    **Faithful port.** Preserve behaviour, edge cases, defaults and naming
    (snake_case of the Zig names). Port doc comments (they are user-visible for