feat(rad): FRA engine phase 2b — mandatory arrival transitions + top-2 repair

Parse Annex 2B mandatory arrival routings and repair the best few
candidates (not just the lowest-error one):

- core::rad: MandatoryArr + RadData.mandatory_arr +
  mandatory_arr_transitions(ades) -> allowed point-sequences.
- rad crate: parse_mandatory_arr() (VIA-clauses in NOT-AVBL-EXC rows,
  scoped to ARR airports). via_sequences() now scans all parenthesised
  transition groups (contain DCT/airway), not just contiguous "VIA (",
  because sub-option markers separate them ("VIA i) (KARDU DCT KALMO)").
  rad-tool `manarr [ADES]`. LIML now yields KARDU KALMO etc.
- discover: "manarr" candidates route to the transition's on-airway
  anchor then splice the (often off-airway) transition points in via DCT.
- attempt_once repairs the top-2 candidates and keeps the best result:
  the lowest-raw-error candidate isn't always the most repairable (a
  mandate-satisfying route may carry more mechanical errors than a route
  stuck on an unfixable mandatory).

Collapses the dense-FRA near-misses: EGLL-EDDM 7->1 err, EDDF-LIRF 3->1
(mandatory PROF205 resolved; residual is a single ROUTE49). Coverage 6/10,
no regression (passing pairs short-circuit on accept). 49 tests green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/rad/src/lib.rs

@@ -10,7 +10,8 @@ use calamine::{open_workbook, Data, Reader, Xlsx};
 // The RAD data model lives in `core` (so routing/validation can use it without
 // pulling in `calamine`); this crate produces those types.
 pub use flightplanner_core::rad::{
-    Area, DctKind, DctRestriction, ForbiddenSeg, FraEdge, FraPoint, LevelCap, MandatoryDep, RadData,
+    Area, DctKind, DctRestriction, ForbiddenSeg, FraEdge, FraPoint, LevelCap, MandatoryArr,
+    MandatoryDep, RadData,
 };
 
 /// Parse the official EUROCONTROL "FRA Points" list (a separate `.xlsx` — see the
@@ -119,9 +120,35 @@ pub fn parse(path: &str) -> Result<RadData> {
         fra_points: Vec::new(), // loaded separately via parse_fra_points
         forbidden_segs: parse_forbidden_segments(path)?,
         mandatory_dep: parse_mandatory_dep(path)?,
+        mandatory_arr: parse_mandatory_arr(path)?,
     })
 }
 
+/// Annex 2B — mandatory arrival routings. Rows whose utilization lists allowed
+/// `VIA (...)` transitions as exceptions to a `NOT AVBL FOR TFC` ban, scoped to
+/// one or more `ARR <airport>`s (e.g. LI2137: `ARR LIML VIA (KARDU DCT KALMO)`).
+/// v1 associates every VIA-sequence in a row with every ARR airport in it (the
+/// DEP gating is dropped — candidates are additive, so the oracle filters).
+pub fn parse_mandatory_arr(path: &str) -> Result<Vec<MandatoryArr>> {
+    let Ok(rows) = rows(path, "Annex 2B") else {
+        return Ok(Vec::new());
+    };
+    let mut out = Vec::new();
+    for r in rows.iter().skip(1) {
+        let up = cell(r, 8).to_uppercase().replace(['\r'], " ");
+        if !up.contains("NOT AVBL FOR TFC") || !up.contains("ARR ") || !up.contains("VIA (") {
+            continue;
+        }
+        let airports = apt_after(&up, "ARR");
+        let allowed: Vec<Vec<String>> = via_sequences(&up).into_iter().filter(|s| !s.is_empty()).collect();
+        if airports.is_empty() || allowed.is_empty() {
+            continue;
+        }
+        out.push(MandatoryArr { id: cell(r, 3), airports, allowed });
+    }
+    Ok(out)
+}
+
 /// Annex 3A DEP — mandatory departure routings (`COMPULSORY FOR TFC`). Extracts
 /// the allowed transition point-sequences from the `VIA (...)` clauses, chaining
 /// sub-fragments (`d. VIA (OPALE DCT KESAX)` + `ii) VIA (KESAX DCT DIMAL DCT
@@ -151,14 +178,20 @@ pub fn parse_mandatory_dep(path: &str) -> Result<Vec<MandatoryDep>> {
     Ok(out)
 }
 
-/// The point-sequences inside every `VIA (...)` clause (balanced parens), dropping
-/// `DCT`/airways/keywords — just the ordered enroute points.
+/// Point-sequences from every parenthesised transition clause (balanced parens
+/// that contain a `DCT` or an airway token — which skips airport lists like
+/// `(LIMJ, LIRP)` and engine-type notes like `(J)`). We can't anchor on `VIA (`
+/// because sub-option markers separate them (`VIA i) (KARDU DCT KALMO)`).
 fn via_sequences(up: &str) -> Vec<Vec<String>> {
     let bytes = up.as_bytes();
     let mut out = Vec::new();
     let mut i = 0;
-    while let Some(p) = up[i..].find("VIA (") {
-        let start = i + p + 5;
+    while i < bytes.len() {
+        if bytes[i] != b'(' {
+            i += 1;
+            continue;
+        }
+        let start = i + 1;
         let mut depth = 1;
         let mut j = start;
         while j < bytes.len() && depth > 0 {
@@ -170,7 +203,15 @@ fn via_sequences(up: &str) -> Vec<Vec<String>> {
             j += 1;
         }
         let inner = &up[start..j.saturating_sub(1)];
-        out.extend(expand_via(inner));
+        let is_transition = inner.split(|c: char| !c.is_ascii_alphanumeric()).any(|t| {
+            t == "DCT"
+                || (t.len() >= 2
+                    && t.chars().next().is_some_and(|c| c.is_ascii_alphabetic())
+                    && t.chars().any(|c| c.is_ascii_digit()))
+        });
+        if is_transition {
+            out.extend(expand_via(inner));
+        }
         i = j;
     }
     out

crates/rad/src/main.rs

@@ -186,7 +186,20 @@ fn main() -> Result<()> {
                 }
             }
         }
-        _ => println!("usage: rad-tool sheets | dump | find | summary | fra [point] | caps [FROM TO] | frapts [file] [POINT] | forbidden [ADEP ADES FL] | mandep [ADEP]"),
+        Some("manarr") => {
+            // manarr [ADES] — mandatory arrival transitions (Annex 2B).
+            let rad = flightplanner_rad::parse(&path)?;
+            println!("Mandatory arrival routings (Annex 2B): {}", rad.mandatory_arr.len());
+            if let Some(a) = args.get(2) {
+                let a = a.to_uppercase();
+                let seqs = rad.mandatory_arr_transitions(&a);
+                println!("{a}: {} allowed transition sequences", seqs.len());
+                for s in seqs.iter().take(40) {
+                    println!("    {}", s.join(" "));
+                }
+            }
+        }
+        _ => println!("usage: rad-tool sheets | dump | find | summary | fra [point] | caps [FROM TO] | frapts [file] [POINT] | forbidden [ADEP ADES FL] | mandep [ADEP] | manarr [ADES]"),
     }
     Ok(())
 }