Drift now takes &T -> &T and is generic over the time axis. Untimed
impls return elapsed=0. ConstantDrift impl covers all T via the Time
trait. An additional variance_for_elapsed(i64) method on the trait
serves callers that work with the pre-cached i64 elapsed count.
Competitor.last_time moves from i64 with MIN sentinel to Option<T>
with None sentinel. receive(&T) computes variance from last_time
dynamically; receive_for_elapsed(i64) uses a pre-cached elapsed count
(needed in convergence sweeps where last_time has already advanced).
TimeSlice.time changes from i64 to T. compute_elapsed is now generic
over T and takes Option<&T> for the last-seen time. new_forward_info
uses receive_for_elapsed to preserve the cached elapsed during sweeps.
History<D> becomes History<T, D>; HistoryBuilder<D> becomes
HistoryBuilder<T, D>; Game<D> becomes Game<T, D>. Defaults keep
existing call sites compiling with zero changes: T = i64,
D = ConstantDrift.
add_events / add_events_with_prior stay on impl History<i64, D> since
times: Vec<i64> is i64-specific (Task 8 will generalise this).
In !self.time mode the old i64::MAX sentinel guaranteed elapsed=1 for
every slice transition regardless of time gaps. Replaced by advancing
all previously-seen agents' last_time to Some(current_slice_time) at
the end of each slice; this preserves elapsed=1 between adjacent
slices in sequential-integer untimed mode.
The time: bool field on History and .time(bool) on HistoryBuilder are
NOT removed by this task — deferred to Task 8 so this commit is
purely a type-level generification.
Part of T2 of docs/superpowers/specs/2026-04-23-trueskill-engine-redesign-design.md.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
The struct holds prior/beta/drift — a rating configuration, not a
person. The person-with-temporal-state is the Competitor (renamed in
the next task). Resolves Player/Agent ambiguity.
Part of T2 of docs/superpowers/specs/2026-04-23-trueskill-engine-redesign-design.md.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Move team_prior, lhood_lose, lhood_win, inv_buf into ScratchArena so
their Vec capacity is reused across games in a Batch. Eliminates 5
per-game heap allocations (the trunc Vec remains local due to borrow
constraints with arena.vars).
Batch::iteration: 23.0 µs (down from 27.0 µs with naive local Vecs;
8% above T0 21.253 µs baseline due to TruncFactor propagate overhead).
Game::likelihoods now uses VarStore (for diff vars) and TruncFactor
(for EP truncation + evidence caching) instead of TeamMessage and
DiffMessage. The EP loop structure is preserved exactly; VarId-keyed
diff vars live in the arena's VarStore (capacity reused per batch).
ScratchArena loses teams/diffs/ties/margins; gains VarStore and
sort_buf (sort_perm allocation eliminated). message.rs deleted.
Public API of Game (new, posteriors, likelihoods, evidence) unchanged.
Game::likelihoods previously allocated four Vecs (teams, diffs, ties,
margins) on every call. Batch now owns one ScratchArena reused across
all Game::new calls in the iteration loop; likelihoods() clears and
extends the arena buffers instead of allocating fresh.
For log_evidence (called infrequently), a local ScratchArena is created
per invocation so the method signature stays &self.
Also: add #[derive(Debug)] to TeamMessage and DiffMessage (required by
ScratchArena's own Debug derive).
Part of T0 engine redesign.
Mul and Div become two f64 adds/subs with no sqrt in the hot path.
mu() and sigma() are computed on demand from stored pi/tau.
Key implementation notes:
- exclude() returns N00 when var <= 0 to avoid inf/inf = NaN when
two Gaussians have the same precision (ULP-level round-trip error
from the pi→sigma accessor).
- Mul<f64> by 0.0 returns N00 (point mass at 0), matching old behavior.
- from_ms(0, 0) == N00 {pi:inf, tau:0}; from_ms(0, inf) == N_INF {pi:0, tau:0}.
Golden values in test_1vs1vs1_draw updated: nat-param arithmetic
rounds mu to 25.0 (was 24.999999) and shifts sigma by ~3e-7.
Both differences are bounded and validated against the original Python
reference values.
Part of T0 engine redesign.
