fix(walk): the cycle starts at maximum stride, so the capture shows one

The stride shot regressed twice for two different reasons, and only the second was
the clip. The walk cycle was authored on a sine, which is zero at both the start and
the middle of the cycle - exactly the two frames where the legs pass together - so a
deterministic capture at any phase near those frames read as a still. The probe
proved it: frames 0 and 15 carried identical hip rotations while 7 and 22 were the
stride.

The cycle now starts at maximum stride (cosine). Length, amplitudes, keys and loop
are unchanged; only the phase moved. demo-third-person-walk is back as shot 8 and
shows a genuine stride with the curled hands from 0.2.1.

8/8 shots verify.

Screenshots/README.md

@@ -132,6 +132,19 @@ What it shows: the arms hang down with a soft elbow bend, the hands sit at hip h
 
 ---
 
+## 8. Third-person walk
+
+![Third-person walk: the body mid-stride in profile](demo/review-demo-third-person-walk.png)
+
+- **File:** `demo/review-demo-third-person-walk.png`
+- **View:** tracking camera, 4.2 m to the pawn's right, captured while the pawn walks south
+- **Expected content:** the body mid-stride in profile — legs apart, arms counter-swinging
+- **Verified:** ☑ 2026-11-09 · **Approved:** ☐ pending
+
+**Why the earlier attempts failed, twice:** the first was a harness problem (a fixed camera cannot catch a pawn at 4.5 m/s, and the call that enables walking ran before the pawn existed). The second was the clip itself: the walk cycle was authored on a **sine**, which is zero at both the start and the middle of the cycle, so the capture kept landing on the two frames where the legs pass together and the image read as a still. The clip now starts at maximum stride (cosine), so any frame near the start shows the stride. The cycle length, amplitudes and loop are unchanged.
+
+---
+
 ## The iteration loop (uncommitted)
 
 `Tools/visual_loop.py` measures each capture against its reference photograph and turns the deltas into modelling actions for the Blender skill packs:
@@ -161,7 +174,6 @@ Every issue is tracked in `TODO.md` under the version that will fix it; an issue
 | Nothing may stand in front of the hero façade that blocks it — no awning, no temporary structure | `0.9.0` → per-building models, hero façade | Open |
 | Retail parapet has no moulded profile, and wall lettering built as a plate does not read at 40 m | `0.9.0` → 6800 Lee Drug and 6806–6820, second pass | Open (moved out of `0.1.6`) |
 | 6822 Budget is a bare blockout volume — no photograph exists to model it from | `0.9.0` → photography gap | Deferred (moved out of `0.1.6`) |
-| The stride shot shows a standing pose again since the finger-curl and derived-arm change; the walk clip plays (`speed=28 clip=GigLine_Walk` in the probe) but the capture lands on a still | `0.2.3` → camera and capture fixes | Open |
 | Camera collision is implemented but never exercised against a wall | `0.2.0` → camera collision | Open |
 | The walk clip has never been captured in motion — it imports and its curves carry the stride, but no shot shows it | `0.2.0` → verify animation plays correctly | Open |
 | Between kerb and building line the walkable surface is the terrain mesh, not a modelled pavement | `0.6.0` → model the pavement between kerb and building line | Open |