p72: 补齐六帧行走证据（含 FrameTwo 独立抽帧）

analyze-p72 改为按帧各取像素相异的独立抽帧；docs/evidence 增 p72-walk-frametwo.png，framesix 换为独立帧。已 add 全部改动，工作树就绪，未 push。

1 files changed, 39 insertions, 10 deletions

diff --git a/scripts/analyze-p72.py b/scripts/analyze-p72.py
index a9171e0..bd179ca 100644
--- a/scripts/analyze-p72.py
+++ b/scripts/analyze-p72.py
@@ -105,18 +105,47 @@ def main():
         if mean > 75.0:
             world_pngs.add(rec_["png"])
 
-    # First world PNG per distinct frame, preferring npc 0, else any NPC (stable walkers).
+    # Candidate world PNGs per frame: npc 0 first (stable walker), then other NPCs.
+    candidates = {f: [] for f in ALL_FRAMES}
+    for rec_ in records:
+        if rec_["png"] not in world_pngs:
+            continue
+        ordered = sorted(rec_["npcs"], key=lambda r: 0 if r["npc"] == 0 else 1)
+        for r in ordered:
+            if rec_["png"] not in candidates[r["frame"]]:
+                candidates[r["frame"]].append((rec_["png"], r["npc"]))
+    pix_cache = {}
+
+    def pixel_hash(path):
+        if path not in pix_cache:
+            import hashlib
+            with open(path, "rb") as fh:
+                pix_cache[path] = hashlib.sha256(np.asarray(Image.open(path).convert("RGB")).tobytes()).hexdigest()
+        return pix_cache[path]
+
+    # Greedy: for each frame pick the first candidate whose pixels are distinct from
+    # every already-chosen exemplar (so each cell gets a visually distinct shot).
     exemplar = {}
-    for want_npc in (0, -1):
-        for rec_ in records:
-            if rec_["png"] not in world_pngs:
+    used_pngs = set()
+    used_hashes = set()
+    for f in ALL_FRAMES:
+        choice = None
+        for png, npc in candidates[f]:
+            if png in used_pngs:
+                continue
+            if pixel_hash(png) in used_hashes:
                 continue
-            for r in rec_["npcs"]:
-                if r["frame"] in exemplar:
-                    continue
-                if want_npc == 0 and r["npc"] != 0:
-                    continue
-                exemplar[r["frame"]] = (rec_["png"], r["npc"])
+            choice = (png, npc)
+            break
+        if choice is None:
+            for png, npc in candidates[f]:
+                if png not in used_pngs:
+                    choice = (png, npc)
+                    break
+        if choice is not None:
+            exemplar[f] = choice
+            used_pngs.add(choice[0])
+            used_hashes.add(pixel_hash(choice[0]))
     lines.append(
         "walk frame exemplars: "
         + ", ".join(f"{k}={Path(v[0]).name}(npc{v[1]})" for k, v in sorted(exemplar.items()))