feat(ring): fast-spin blended pass past a speed threshold (scales design §3)

A multi-detent encoder spin previously chained one full transition per scale
crossed (e.g. +5 ≈ 5 placeholder morphs ≈ 12-15s), which feels sluggish for a
fast spin. Design §3 anticipates this: "transitions chain, or past a speed
threshold a faster blended pass is used."

`player.ring.advance_ring` gains an opt-in `fast_spin_threshold` (canonical
default `DEFAULT_FAST_SPIN_THRESHOLD = 3`). A spin batches its detents into one
advance() call, so `abs(delta)` is the input layer's proxy for spin speed; at or
above the threshold the move collapses to a single blended pass — one
`TransitionStep` (the arrival edge, marked `blended`, landing straight on the
destination, `RingMove.fast=True`) instead of the full chain. Landing index,
seam-crossing (`wrapped`), and arrival edge/direction are exactly the full
chain's; only the in-between transitions are dropped.

The policy is opt-in (default off) because the pure function cannot observe
wall-clock spin speed — the simulator/firmware, which can, enables it. This keeps
all existing complete-chain behavior and tests intact. The simulator passes the
default threshold and plays the blended step at 2.5× (FAST_BLEND_RATE); a
dedicated fast-blend clip can replace the accelerated arrival-edge placeholder
when real transition media exists.

- player/ring.py: TransitionStep.blended, RingMove.fast, threshold param + policy
- simulator/clips.py: serialize fast/blended in ring_move_to_dict
- simulator/app.py: apply DEFAULT_FAST_SPIN_THRESHOLD at /api/ring/advance
- simulator/static/app.js: play a blended step at FAST_BLEND_RATE
- docs: scales design §3, USER_GUIDE, ROADMAP slice-3 note

Tests: +9 (ring policy, serializer, API). Suite 224 passed / 2 skipped.

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

docs/ROADMAP.md

@@ -155,6 +155,10 @@ generated as labelled placeholders by `simulator/setup_scales_media.py`. The
 expensive real multi-strength flow-stabilized Right re-bake is **deferred** (new
 scales carry a raw base only) until the ring is liked. Plan:
 [`2026-06-07-scale-ring-navigation.md`](./superpowers/plans/2026-06-07-scale-ring-navigation.md).
+Session 0012 added the design §3 **fast-spin** behavior on top: past an opt-in
+speed threshold (`DEFAULT_FAST_SPIN_THRESHOLD = 3`, `abs(delta)` as the spin-speed
+proxy) a quick spin collapses to a single **blended pass** instead of chaining
+every transition, so fast navigation stays responsive on placeholder media.
 
 **Remaining slices (not started):**
 

docs/USER_GUIDE.md

@@ -330,7 +330,10 @@ then open http://localhost:8000.
   (an endless encoder), distinct from the absolute 0–4 knobs: each step plays a
   short placeholder zoom/warp **transition**, then settles on the next scale, with
   the current knob alteration still applied. The current scale is named beside the
-  buttons (`name (i/N)`).
+  buttons (`name (i/N)`). A **fast spin** (scroll several detents at once, ≥3)
+  collapses to a single quick **blended pass** straight to the destination scale
+  instead of grinding through every transition (scales design §3); slow single
+  steps still chain one full transition per scale crossed.
 - **Four experience knobs (0–4):**
   - **Dark / Light** — a live runtime color grade (cool/dark ↔ warm/bright; equal
     or zero = the raw footage).

docs/superpowers/specs/2026-06-07-scales-library-and-right-axis-pipeline-design.md

@@ -162,6 +162,17 @@ the ring continuous.
   local; one clip per ring edge (N scales → N transitions, including the micro→cosmos
   closer). A fast spin may cross several scales — transitions chain, or past a speed
   threshold a faster blended pass is used.
+  - **Implemented (session 0012):** `player.ring.advance_ring` takes an opt-in
+    `fast_spin_threshold` (canonical default `DEFAULT_FAST_SPIN_THRESHOLD = 3`).
+    A spin batches its detents into one `advance` call, so `abs(delta)` is the
+    input layer's proxy for spin speed; at/above the threshold the move collapses
+    to a **single blended pass** — one `TransitionStep` (the arrival edge, marked
+    `blended`, landing straight on the destination, `RingMove.fast=True`) instead
+    of chaining every transition. The policy is opt-in because the pure function
+    cannot observe wall-clock speed — the simulator/firmware enables it. The
+    simulator plays the blended step at 2.5× (`FAST_BLEND_RATE`); when real
+    transition clips exist a dedicated fast-blend clip can replace the
+    accelerated arrival-edge placeholder. Threshold + rate are tunable by eye.
 - **Thesis-safe:** dwells on a scale are the neutral, knob-altered interactive cores;
   transitions are fixed connective moments (un-altered, or at most carrying the
   current mood grade). The awe lives in the *movement between* scales, not the base.