docs(rewrite): record final verification RV13

docs/rewrite/notes/review-rv13-codex.md

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+# Codex final verification (RV13, 2026-10-12)
+
+**At `f68b11d`: the three original RV12 reproductions are resolved, but full parity still has four verified P3 gaps.** Counts: **0 P1, 0 P2, 4 P3**. No files were modified; the worktree remains clean.
+
+| RV12 finding | Result |
+|---|---|
+| Platform errno numbering | Fixed: platform constants replace Linux-only numbers. A separate Windows error-mapping defect remains below. |
+| `theme=.` / `theme=..` | Fixed. Basename handling and directory diagnostics now match; the existing `..` fixture matched the installed oracle. |
+| Sprite rasterization | Fixed in the saved evidence: all **36 sprite sheets** and all **three VP scenarios** recompute to **0 differing pixels**. |
+
+The fresh sweep covered the **461-file inventory: 428 non-build files and 33 build files**, checking counterparts, exports, incomplete paths, configuration consumers, and build outputs, with targeted behavioral checks. No wholly absent source counterpart was established. This is breadth coverage, not proof of exhaustive equivalence.
+
+Concrete remaining gaps:
+
+1. **P3 — Wrong default update channel.** [config.rs:4659](/pantheon/pfs/git/rust/ghostty-rewrite/ghostty-rs/target/wt-head/crates/ghostty-config/src/config.rs:4659) hardcodes `Stable`. Both tested binaries report `channel: tip`, but `+show-config` prints `stable` for Rust and `tip` for Zig. Zig defaults this field from the build channel.
+
+2. **P3 — `async-backend` is ineffective.** [application.rs:332](/pantheon/pfs/git/rust/ghostty-rewrite/ghostty-rs/target/wt-head/crates/ghostty-apprt-gtk/src/class/application.rs:332) omits Zig’s backend-selection startup step. The parsed field has no runtime consumer; [thread.rs:234](/pantheon/pfs/git/rust/ghostty-rewrite/ghostty-rs/target/wt-head/crates/ghostty-termio/src/thread.rs:234) uses polling regardless of `epoll` or `io_uring`. Verified statically.
+
+3. **P3 — Windows file-open diagnostics use the wrong error mapping.** [zig_error.rs:101](/pantheon/pfs/git/rust/ghostty-rewrite/ghostty-rs/target/wt-head/crates/ghostty-os/src/zig_error.rs:101) maps sharing violations to `FileBusy`; Zig’s Windows `OpenFile` maps them to `AccessDenied`. Theme loading uses this helper. Verified statically against Zig 0.15.2; native execution unavailable.
+
+4. **P3 — Windows basename handling restricts drive prefixes incorrectly.** [theme.rs:162](/pantheon/pfs/git/rust/ghostty-rewrite/ghostty-rs/target/wt-head/crates/ghostty-config/src/theme.rs:162) requires an alphabetic first byte. For `1:theme`, Rust returns the whole name while Zig returns `theme`, so Rust bypasses Zig’s rejection diagnostic. Verified statically; native execution unavailable.
+
+Fresh validation produced:
+
+- **2,770 tests passed**, four ignored; file-writing tests excluded.
+- **2,000 terminal differential cases matched**, with no aborts.
+- **617 CLI/config comparisons**: 606 exact matches; all 11 mismatches concern the update-channel default.
+- All **138 C/WASM API declarations** have Rust counterparts; WASM smoke test passed.
+
+Existing binaries were reused; no fresh build or visual capture was made. The documented **390,000-case campaign** remains supporting evidence, not a rerun. Genuine Zig memory bugs/UB were excluded.
+
+**Inherently unavailable natively here:** Apple Metal/IOSurface/CoreText, Carbon/AppKit/UIKit, Mach crash handling and Apple packaging; Windows ConPTY/process creation, native filesystem/environment behavior and exception handling.
+
+Fresh Linux compositor/GPU, portal/D-Bus, and interactive GTK checks were not rerun. Those are coverage limitations, not inherently unverifiable Linux functionality.