Fix HD atlas sampling and protected terrain joins

Add rational atlas cells and bounded authenticated Original-detail retention with standalone synthetic regression checks. Rebuild Linux and Windows runtimes; validate all 5384 supplied frames and preserve three exact 1080p regression controls.

tools/hd_frame_policy.py

@@ -1,8 +1,57 @@
 """Strict optional HD presentation metadata; source fidelity requires peer review."""
 import struct
+from fractions import Fraction
 
 FRAME_KEYS = {"frame", "file", "logical_width", "logical_height", "origin",
-              "source_sha256", "crop", "preserve_reserved_coverage", "native_nearest_cues", "original_detail_cells"}
+              "source_sha256", "crop", "atlas_grid", "preserve_reserved_coverage", "native_nearest_cues", "original_detail_cells"}
+
+def validate_atlas_grid(frame):
+    grid = frame.get("atlas_grid")
+    if grid is None:
+        return None
+    if type(grid) is not dict or set(grid) != {"columns", "rows", "column", "row"}:
+        raise ValueError("atlas_grid needs exactly columns/rows/column/row")
+    if any(type(value) is not int or not 0 <= value < 2**32 for value in grid.values()):
+        raise ValueError("atlas_grid fields must be u32 integers")
+    if frame.get("crop") is not None:
+        raise ValueError("atlas_grid and crop are mutually exclusive")
+    if grid["columns"] == 0 or grid["rows"] == 0 or grid["columns"] * grid["rows"] > 16384:
+        raise ValueError("atlas_grid axes or cell count invalid")
+    if grid["column"] >= grid["columns"] or grid["row"] >= grid["rows"]:
+        raise ValueError("atlas_grid cell is outside its declared axes")
+    return grid
+
+def atlas_grid_geometry(frame, width, height):
+    """Exact equal bounds and a bounded, uniform resident2x–4x canvas."""
+    grid = validate_atlas_grid(frame)
+    if grid is None:
+        return None
+    if any(type(value) is not int or value <= 0 for value in [width, height]):
+        raise ValueError("invalid atlas dimensions")
+    lw, lh = frame["logical_width"], frame["logical_height"]
+    if any(type(value) is not int or not 0 < value < 2**32 for value in [lw, lh]):
+        raise ValueError("invalid logical dimensions")
+    cols, rows = grid["columns"], grid["rows"]
+    if width * lh * rows != height * lw * cols:
+        raise ValueError("rational atlas cell aspect differs from original canvas")
+    if width < 2 * cols * lw or height < 2 * rows * lh:
+        raise ValueError("rational atlas cell needs at least twice the logical resolution")
+    factor = min(width // (cols * lw), height // (rows * lh), 4)
+    left, right = Fraction(width * grid["column"], cols), Fraction(width * (grid["column"] + 1), cols)
+    top, bottom = Fraction(height * grid["row"], rows), Fraction(height * (grid["row"] + 1), rows)
+    floor = lambda value: value.numerator // value.denominator
+    ceil = lambda value: -(-value.numerator // value.denominator)
+    return dict(bounds=(left, top, right, bottom),
+                pixels=(floor(left), floor(top), ceil(right), ceil(bottom)),
+                resident=(lw * factor, lh * factor))
+
+LEGACY_RETAINED_POLICY = "retained-original-details-v2-painted0255"
+EXTENDED_RETAINED_POLICY = "retained-original-details-v3-max128-quarter-painted0255"
+
+def retained_review_version_ok(version, retained_details):
+    """The old declaration cannot authorize a new longer list; old bytes stay valid."""
+    return version == EXTENDED_RETAINED_POLICY or (version == LEGACY_RETAINED_POLICY
+            and all(len(cells) <= 64 for cells in retained_details.values()))
 
 def _indices(payload):
     if len(payload) < 20:
@@ -40,6 +89,7 @@ def _indices(payload):
 def validate_frame_policy(frame, source_payload=None):
     if set(frame) - FRAME_KEYS:
         raise ValueError("unknown HD frame fields")
+    validate_atlas_grid(frame)
     if type(frame.get("preserve_reserved_coverage", False)) is not bool:
         raise ValueError("preserve_reserved_coverage must be a boolean")
     cues = frame.get("native_nearest_cues", [])
@@ -68,8 +118,8 @@ def validate_frame_policy(frame, source_payload=None):
             raise ValueError("native nearest cue must be an ordinary original source cell")
 
     details = frame.get("original_detail_cells", [])
-    if type(details) is not list or len(details) > 64:
-        raise ValueError("original_detail_cells must contain at most64 Source cells")
+    if type(details) is not list or len(details) > 128:
+        raise ValueError("original_detail_cells must contain at most128 Source cells")
     previous = None
     for cell in details:
         if type(cell) is not list or len(cell) != 2 or any(type(n) is not int or not 0 <= n < 2**32 for n in cell):
@@ -86,3 +136,8 @@ def validate_frame_policy(frame, source_payload=None):
             raise ValueError("Original detail canvas differs from Source")
         if any(not 0 <= indices[y * width + x] < 256 for x, y in details):
             raise ValueError("Original details select painted Source indices0–255 only")
+
+        # Metadata-only preparation can check structure, not claim Source density.
+        # Runtime, audit and extended registrar approval supply actual payloads.
+        if len(details) > 64 and len(details) * 4 > sum(0 <= p <= 255 for p in indices):
+            raise ValueError("65..128 Original details may retain at most one quarter of painted Source")