error: re-export is_halt + is_skippable_title_stub at crate root

The engine's multi-title rip loop classifies per-title mux failures (halt vs
skippable stub vs hard) using these typed classifiers instead of E-code string
matching. Additive; no behavior change.

src/lib.rs

@@ -155,7 +155,7 @@ pub use session::{
 // All fallible APIs return `Result<T, Error>`. `Error` is a typed enum with a
 // numeric `code()`; **no English text in the library** — applications map
 // codes to localized messages. See `error.rs` for the full taxonomy.
-pub use error::{Error, Result};
+pub use error::{Error, Result, is_halt, is_skippable_title_stub};
 
 // ─── Cooperative cancellation ───────────────────────────────────────────────
 //