fix(simulation): PR #191 review round — n-clamp mirror, min_wl band quantization, coalescing coverage, fixture consumer

All seven Hoshe/Tyre findings addressed, none retracted:
- n-clamp/echo/staleness triangle (Tyre C1): client _clamp_window_n_mirror
  (bit-for-bit twin of the server clamp, canonicalize_district_center
  precedent) applied before _n is stored/sent; server test pins the
  quarter n=32 -> echo 16 contract.
- min_wl band quantization (Hoshe 1/Tyre C3): quantize_min_wl_m snaps to
  MIN_WL_BANDS_M {0, 32768, 16384, 8192, 4096} before cache key and echo
  (design doc §5's unbounded-key fix), reusing the one true
  OCTAVE_WAVELENGTHS_M array; docstrings now state the server-quantizes/
  client-sends-raw split; same-band cache-sharing test.
- coalescing granularity axis (Hoshe 2): two tests pin different-
  granularity requests as separate in-flight slots and same-granularity
  coalescing unchanged.
- orphaned fixture (Hoshe 3): test_protocol.gd consumer decodes
  atlas_response_ready_with_window.msgpack through the real IPC path and
  asserts the new fields.
- atlas_window_request coverage (Hoshe 4): new test file — stale-drop on
  granularity mismatch, old-server-shape defaults accepted, clamp mirror
  formula + wiring. First draft's quarter-via-request_now test would have
  passed for the wrong reason (request_now resets granularity by design
  until T-1153) — split into formula pin + reachable-path wiring proof.
- granularity type seam (Tyre C2): field + resolver docstrings state
  finer-only integer multiples with resolve_window_granularity as the
  single widening point; matching contract note added to the D-226
  T-1143-rulings amendment.

cargo --lib 1807/1807; goldens bit-identical; gdlint clean.

client/scripts/protocol/atlas_map_protocol.gd

@@ -39,6 +39,16 @@ class_name AtlasMapProtocol
 ## requests quarter granularity yet (that's T-1153); this function just makes
 ## it possible to ask, byte-compatible with every existing caller that
 ## doesn't pass them.
+##
+## **Quantization split (PR #191 review, Hoshe 1 / Tyre C3):** `window_min_wl_m`
+## is sent HERE as a raw, unquantized value — this codec does NOT snap it to
+## the design doc §5 fixed band set. The SERVER is the one place quantization
+## happens (`serve_district_window` → `quantize_min_wl_m`, `layer_proxy.rs`):
+## it snaps every request's value to the nearest band before touching the
+## cache key or the echo, so a caller here is free to send a
+## viewport-continuous estimate (e.g. `E/C` from the rung-selection rule) —
+## don't pre-quantize client-side, it would just duplicate logic the server
+## already owns and could drift out of sync with it.
 static func encode_atlas_layer_request(
 	mp,
 	body_id: String,