fix(client): PR #192 review round — per-rung legend, Region coalescing + clamp boundary tests, halving-loop honesty

All Hoshe/Araminta findings addressed (Tyre approved outright), none
retracted — plus a Dudley stop-and-flag discovery that improved on the
asked-for fix:

- Legend 100x lie (Araminta, blocking): subtitle computed via
  spacing_for_rung() and refreshed at all three _held_granularity_v2
  write sites. Region test asserts 204.800 km/cell; the District
  direction needed a stale-header-aware helper — a District-only test
  spuriously passes against the old literal by coincidence.
- Region coalescing coverage (Hoshe 1): both directions tested
  (Region-vs-District separate slots; Region-vs-Region coalesces).
- Clamp boundary tests + dangling citations (Hoshe 2): writing the
  requested halving-loop-fires test surfaced that the loop is PROVABLY
  UNREACHABLE at current constants (per-axis clamp forecloses it —
  brute-forced independently on both server and client sides). Ruling:
  the loop stays as defensive code; the test became a property sweep
  pinning both the wire-cap invariant and the loop's no-op status (a
  future constant change breaks it loudly); doc comments on both sides
  drop the load-bearing framing and state the truth; the old client
  mirror test that claimed the loop fires (passing on the per-axis
  clamp alone) is replaced the same way. Client citations now name the
  real server tests verbatim.
- Governance (Tyre): D-226 amendment note — progressive cross-rung
  refinement EXTENDS T-1124 §4 (not supersedes); legacy u32 field
  scheduled for retirement (T-1159).

Server: 1818 lib tests green, clippy/fmt clean. Client: zoom_ladder
48/48, window_request 26/26, viewer 74/74; gdlint clean. Every fix
revert-verified.

server/src/atlas/gen_queue.rs

@@ -1364,6 +1364,76 @@ mod tests {
         );
     }
 
+    /// **PR #192 review — Hoshe 1: zero coalescing coverage for
+    /// `WindowGranularity::Region` before this test**, despite Region being
+    /// the highest-fan-out path (progressive capped-density tiling fires
+    /// multiple concurrent Region `DeriveWindow` items per pan/zoom). Mirrors
+    /// `submit_window_does_not_coalesce_different_granularity`'s pattern
+    /// exactly, substituting Region for Quarter: a Region request and a
+    /// District request for the SAME `(connection, body)` are separate
+    /// in-flight slots (the coalescing key is `(conn_id, body_id,
+    /// granularity)`) and must NOT coalesce — both survive as independent
+    /// pending items.
+    #[test]
+    fn submit_window_does_not_coalesce_region_and_district() {
+        let q = GenerationQueue::with_threads(1);
+        // See `submit_window_coalesces_same_connection_and_body`'s comment on
+        // why the occupier must be `analyze()`, not `FillChunk`.
+        q.submit(analyze("Occupier5"), GenPriority::Low);
+
+        let conn = ConnectionId(13);
+        q.submit_window(
+            derive_window_at("OrbitalGranBody", conn, (0, 0), WindowGranularity::Region),
+            GenPriority::Immediate,
+        );
+        q.submit_window(
+            derive_window_at("OrbitalGranBody", conn, (0, 0), WindowGranularity::District),
+            GenPriority::Immediate,
+        );
+        assert_eq!(
+            q.pending_count(),
+            2,
+            "same (connection, body) but Region vs. District must NOT coalesce — \
+             separate in-flight slots, same as the existing District/Quarter pair"
+        );
+    }
+
+    /// The coalescing-DOES-happen counterpart to the test above, for Region
+    /// specifically: two submissions for the SAME `(connection, body,
+    /// Region)` still collapse to one pending item — confirms Region's
+    /// coalescing key behaves identically to District/Quarter's, not just
+    /// that it avoids cross-granularity aliasing.
+    #[test]
+    fn submit_window_coalesces_same_connection_body_and_region_granularity() {
+        let q = GenerationQueue::with_threads(1);
+        q.submit(analyze("Occupier6"), GenPriority::Low);
+
+        let conn = ConnectionId(15);
+        q.submit_window(
+            derive_window_at(
+                "SameOrbitalGranBody",
+                conn,
+                (0, 0),
+                WindowGranularity::Region,
+            ),
+            GenPriority::Immediate,
+        );
+        q.submit_window(
+            derive_window_at(
+                "SameOrbitalGranBody",
+                conn,
+                (5, 5),
+                WindowGranularity::Region,
+            ),
+            GenPriority::Immediate,
+        );
+        assert_eq!(
+            q.pending_count(),
+            1,
+            "same (connection, body, Region) must still coalesce to one pending item"
+        );
+    }
+
     // -------------------------------------------------------------------
     // TerrainAnalysisCache (T-1137, PR #187 review — Tyre C1)
     // -------------------------------------------------------------------