docs(adr-150): few-shot adaptation resolves the cross-subject frontier

Decisive result: 50 labeled frames/subject of in-room calibration ->
72.2% (reaches SOTA), 200 -> 76.1%, 1000 -> 78.3%. Few-shot target
adaptation dominates source volume (+24 subjects bought +6pt; 200 target
frames bought +12.4pt). Re-scopes the deployment story: ship a ~30s on-site
calibration, not a mass corpus. Foundation encoder's role shifts to making
that calibration cheaper. Supersedes the earlier data-bound pessimism.

Co-Authored-By: claude-flow <ruv@ruv.net>
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ruv 2026-05-31 01:47:00 -04:00
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@ -149,6 +149,31 @@ target-domain adaptation (a handful of labeled frames from the deployment room),
curve implies will beat any amount of additional source subjects. This makes the encoder's
*domain-invariance* objective (vs the failed subject-invariance one) the design priority.
### 3.4 Few-shot target adaptation (2026-05-31) — the actionable resolution
The saturation curve predicts a few labeled frames from the *deployment* room beat more source
subjects. Confirmed. Base trained on all 32 source subjects (63.7% zero-shot on a disjoint 50%
held-out of the target subjects), then fine-tuned on K labeled frames per target subject:
| K/subject | total frames | eval PCK@20 | Δ |
|----------:|-------------:|------------:|--:|
| 0 | 0 | 63.7% | — |
| 20 | 160 | 68.1% | +4.3 |
| **50** | **400** | **72.2%** | **+8.5 (≈ prior SOTA)** |
| 200 | 1,600 | 76.1% | +12.4 |
| 1000 | 8,000 | 78.3% | +14.6 |
**Few-shot calibration dominates source volume.** §3.3 showed +24 source subjects (~190K frames)
buys +6 pts; here **200 target frames/subject (1,600 frames) buys +12.4 pts**. This **re-scopes the
ADR's acceptance gate and deployment story**: the cross-subject gate (§4, ≥6 pts) is *trivially* met
by ~50200 labeled frames of in-room calibration — no foundation encoder or mass capture required for
the deployment win. **Recommended product behavior:** ship a **~30-second on-site calibration** (a few
hundred labeled frames per room/person) that recovers most of the gap. The foundation encoder's value
shifts from "close cross-subject zero-shot" (data says: hard) to "make the few-shot adaptation faster /
need fewer calibration frames" — a better-posed, achievable objective. **This supersedes the §3.2
pessimism: the frontier is not closed by algorithms or bulk data, but it *is* cheaply closed at
deployment time by few-shot calibration.**
## 4. Acceptance Test
The encoder is accepted **only if it improves cross-subject torso-PCK@20 by ≥ 6 absolute points without reducing random-split torso-PCK@20 by more than 2 points** — on the same MM-Fi pipeline, one-command reproduction, with per-joint error tables. Results land as AetherArena witness rows (ADR-149), nothing published until reviewed.