feat: implement RobertEngine — Lafayette fabric physics core

[Copilot]

Adds the RobertEngine Python class implementing fabric physics for garment overlay rendering in the Lafayette mirror, computing render metrics purely from detected biometric volumetry (no user-input weight/height required).

New: api/robert_engine.py

• calculate_lafayette_factor(fabric) — silhouette width amplification: 2.2 + (0.5 − drapeCoeff × 0.4)
• calculate_gravity_stretch(fabric, torso_h) — height elongation from GSM weight, normalised to 50–400 range, capped at +15%
• calculate_dynamic_alpha(fit_score, fabric, timestamp) — alpha 0.95 at perfect fit (≥95%), otherwise 0.85 ± sinusoidal breathing pulse, clamped to [0.65, 0.95]
• get_render_metrics(fabric_key, shoulder_w, torso_h, fit_score) — main API combining the above into {width, height, alpha, is_shiny, is_scanning, patent_id}

Pilot fabric catalogue includes silk_haussmann, business_elite, velvet_marais, linen_bastille, jersey_opera.

Bug fix

Reference code used if not timestamp: which treats the valid timestamp 0.0 as missing, silently falling back to time.time(). Changed to if timestamp is None:.

# Before — broken for timestamp=0.0
if not timestamp:
    timestamp = time.time() * 1000

# After
if timestamp is None:
    timestamp = time.time() * 1000

New: tests/test_robert_engine.py

32 unit tests across 4 classes covering the fabric catalogue, each calculation method (boundary conditions, clamping, cross-fabric ordering), and the full get_render_metrics output including the exact values from the problem statement's reference example.

[vercel]

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Project	Deployment	Actions	Updated (UTC)
tryonyou-pilot	Error		Apr 7, 2026 1:37pm