Replace _Signal class (Python) and SxSignal constructor (JS) with plain
dicts keyed by "__signal". Nine platform accessor functions become ~20
lines of pure SX in signals.sx. type-of returns "dict" for signals;
signal? is now a structural predicate (dict? + has-key?).
Net: -168 lines platform, +120 lines SX. Zero platform primitives for
reactivity — signals compile to any host via the bootstrappers.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Reactive tracking (deref/computed/effect dep discovery) and island lifecycle
now use the general scoped effects system instead of parallel infrastructure.
Two scope names: "sx-reactive" for tracking context, "sx-island-scope" for
island disposable collection. Eliminates ~98 net lines: _TrackingContext class,
7 tracking context platform functions (Python + JS), *island-scope* global,
and corresponding RENAME_MAP entries. All 20 signal tests pass (17 original +
3 new scope integration tests), plus CEK/continuation/type tests clean.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
