First sub-project of the "make contact feel real" arc (spec:
docs/superpowers/specs/2026-07-23-possession-presentation-design.md).
Direct Contact replies now feel like a spirit fighting through static to
hold the channel rather than a plain chat bubble:
- backend/app/possession.py: compute_stability(rarity, magnitude, rng) —
a 0.05-0.98 score per reply (rarer entity + stronger triggering anomaly =
cleaner signal), rng injectable for a later quantum-RNG source.
- ws.py sends stability on reply_start; audio synthesis for that reply gets
noise/bitcrush scaled by instability (1 - stability) via a new
instability param on synthesize_spirit_voice — effects.py itself is
untouched, only the params fed into it.
- frontend/src/lib/possession.ts: renderPossessedText — pure, deterministic
(tick-seeded, no Math.random) text corruption with self-correcting
glitch bursts, wired into Transcript.tsx's streaming reply display.
Stored transcript/reply text is unaffected — this is presentation only.
78/78 backend, 137/137 frontend tests passing.
