Under #[cfg(feature = "rayon")], the per-iteration event sweep
processes events color-by-color: within a color, events touch
disjoint Index values by construction, so par_iter is safe.
Across colors, sequential ordering preserves async-EP semantics.
Event::compute() is a pure function returning an owned EventOutput
(new per-item likelihoods, evidence, and pre-computed new skill
likelihoods). The apply phase runs sequentially after the parallel
map, writing EventOutput values back to SkillStore and each event's
item likelihoods. This avoids shared mutable state in the hot loop.
Default build (no rayon) uses a sequential fallback that traverses
the same color-group order — behaviorally identical to the parallel
path. This keeps goldens bit-identical across feature configurations.
Scenario 3b applied: event updates read from and write to the shared
SkillStore, so the compute/apply split (Option A) was necessary.
Part of T3 of docs/superpowers/specs/2026-04-23-trueskill-engine-redesign-design.md.
TimeSlice gains a color_groups field of type ColorGroups, recomputed
whenever events change. After recompute, self.events is physically
reordered so color-0 events are first, then color-1, etc. Each color
is therefore a contiguous range of indices in self.events —
the invariant that Task 6's parallel par_iter_mut exploits.
Greedy coloring via crate::color_group::color_greedy; agent indices
come from Event::iter_agents. ColorGroups gains a color_range helper
that returns the contiguous Range<usize> for a given color.
Numerical behavior unchanged: async-EP is order-independent at
convergence, so event reordering does not affect goldens.
Part of T3.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
ColorGroups holds a partition of event indices into color groups such
that events of the same color touch no shared Index. Computed greedily
in ingestion order: each event goes into the first color whose existing
members are disjoint from the event's indices.
Used in T3 for safe within-slice parallelism — events in the same
color can run concurrently without touching each other's skills.
Part of T3 of docs/superpowers/specs/2026-04-23-trueskill-engine-redesign-design.md.
Required for T3 rayon-based parallelism. Affected traits:
- Time (+ Send + Sync + 'static)
- Drift<T> (+ Send + Sync)
- Observer<T> (+ Send + Sync)
- Factor (+ Send + Sync)
- Schedule (+ Send + Sync)
All built-in impls (i64, Untimed, ConstantDrift, NullObserver,
EpsilonOrMax, TeamSumFactor, RankDiffFactor, TruncFactor,
BuiltinFactor) naturally satisfy these bounds via auto-derive.
Minor breaking change: downstream custom impls that aren't already
thread-safe will need to add the bounds.
Part of T3 of docs/superpowers/specs/2026-04-23-trueskill-engine-redesign-design.md.
Opt-in feature flag — users who want parallel paths build with
--features rayon. Default build remains single-threaded.
Spec Section 6 calls for default-on; we defer that flip until the
feature is stable under field use.
Part of T3 of docs/superpowers/specs/2026-04-23-trueskill-engine-redesign-design.md.
11-task plan for rayon-backed within-slice parallelism per
Section 6 of docs/superpowers/specs/2026-04-23-trueskill-engine-redesign-design.md.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
