feat(ring,api): pick destination clip then resolve matching chained morph

Tasks 3-6. Transition is now a directed clip-pair morph; ScaleRing.morph_for
looks up (from,to)->file. advance_ring returns structural steps (no file);
resolve_move picks each crossed altitude's clip THEN its morph, chained, and
reports the locked target. Fast spin keeps the whole chain (blended) instead
of collapsing. /api/ring/advance takes from_clip_id, draws picks, returns the
resolved chain. Dropped ring_move_to_dict + _rev_file.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_clips.py

@@ -2,12 +2,12 @@ import json
 
 import pytest
 
-from player.ring import RingMove, ScaleRing, TransitionStep, advance_ring
+from player.ring import RingMove, ScaleRing, advance_ring, resolve_move
 from simulator.clips import (
     Clip,
     load_manifest,
     load_ring,
-    ring_move_to_dict,
+    resolved_move_to_dict,
     ring_to_dict,
 )
 
@@ -86,9 +86,12 @@ def _ring_manifest_dict():
                 {"id": "abyss", "clip_id": "abyss"},
             ],
             "transitions": [
-                {"file": "transitions/cosmos-forest.mp4", "model": "placeholder"},
-                {"file": "transitions/forest-abyss.mp4", "model": "placeholder"},
-                {"file": "transitions/abyss-cosmos.mp4", "model": "placeholder"},
+                {"from": "cosmos", "to": "forest", "file": "transitions/cosmos__forest.mp4", "model": "placeholder"},
+                {"from": "forest", "to": "cosmos", "file": "transitions/cosmos__forest.rev.mp4", "model": "placeholder"},
+                {"from": "forest", "to": "abyss", "file": "transitions/forest__abyss.mp4", "model": "placeholder"},
+                {"from": "abyss", "to": "forest", "file": "transitions/forest__abyss.rev.mp4", "model": "placeholder"},
+                {"from": "abyss", "to": "cosmos", "file": "transitions/abyss__cosmos.mp4", "model": "placeholder"},
+                {"from": "cosmos", "to": "abyss", "file": "transitions/abyss__cosmos.rev.mp4", "model": "placeholder"},
             ],
         },
     }
@@ -102,7 +105,8 @@ def test_load_ring_builds_a_scale_ring(tmp_path):
     assert len(ring) == 3
     assert ring.scales[0].id == "cosmos"
     assert ring.scales[0].clip_id == "cosmos"
-    assert ring.transitions[2].file == "transitions/abyss-cosmos.mp4"
+    assert ring.morph_for("abyss", "cosmos") == "transitions/abyss__cosmos.mp4"   # zoom in (wrap)
+    assert ring.morph_for("cosmos", "forest") == "transitions/cosmos__forest.mp4"
     assert ring.transitions[0].model == "placeholder"
 
 
@@ -127,32 +131,39 @@ def test_ring_to_dict_carries_scale_titles_from_clips(tmp_path):
     assert [s["id"] for s in d["scales"]] == ["cosmos", "forest", "abyss"]
     assert d["scales"][0]["title"] == "NASA cosmos"
     assert d["scales"][0]["clip_id"] == "cosmos"
-    assert d["transitions"][2]["file"] == "transitions/abyss-cosmos.mp4"
+    assert d["transitions"][0] == {
+        "from": "cosmos", "to": "forest",
+        "file": "transitions/cosmos__forest.mp4", "model": "placeholder",
+    }
 
 
-def test_ring_move_to_dict_serializes_steps(tmp_path):
+def test_resolved_move_to_dict_serializes_chained_morphs(tmp_path):
     p = tmp_path / "manifest.json"
     p.write_text(json.dumps(_ring_manifest_dict()))
     ring = load_ring(p)
     move = advance_ring(ring, from_index=2, delta=1)  # abyss -> wrap -> cosmos
-    d = ring_move_to_dict(move, ring)
+    resolved = resolve_move(ring, move, from_clip_id="abyss", picks=(0.0,))
+    d = resolved_move_to_dict(move, resolved)
     assert d["from_index"] == 2
     assert d["to_index"] == 0
     assert d["wrapped"] is True
     assert d["target_clip_id"] == "cosmos"
-    assert d["steps"][0]["file"] == "transitions/abyss-cosmos.mp4"
-    assert d["steps"][0]["reversed"] is False
+    assert d["steps"][0]["from_clip"] == "abyss"
+    assert d["steps"][0]["to_clip"] == "cosmos"
+    assert d["steps"][0]["file"] == "transitions/abyss__cosmos.mp4"   # zoom in (wrap)
     assert d["steps"][0]["to_index"] == 0
     assert d["fast"] is False
     assert d["steps"][0]["blended"] is False
 
 
-def test_ring_move_to_dict_marks_fast_blended_pass(tmp_path):
+def test_resolved_move_to_dict_marks_fast_blended_chain(tmp_path):
     p = tmp_path / "manifest.json"
     p.write_text(json.dumps(_ring_manifest_dict()))
     ring = load_ring(p)
     move = advance_ring(ring, from_index=0, delta=4, fast_spin_threshold=3)
-    d = ring_move_to_dict(move, ring)
+    resolved = resolve_move(ring, move, from_clip_id="cosmos",
+                            picks=tuple(0.0 for _ in move.steps))
+    d = resolved_move_to_dict(move, resolved)
     assert d["fast"] is True
-    assert len(d["steps"]) == 1
-    assert d["steps"][0]["blended"] is True
+    assert len(d["steps"]) == 4                       # whole chain kept, played fast
+    assert all(s["blended"] for s in d["steps"])