Phase 5 — Parallelism & Determinism

Authoritative spec. See also the phase index, perf-dod, and testing-strategy. Live issue numbers: pinned master #810.

Expansion: Phase 5 adds ENG2-P5-07 (per-frame frame-arena allocator + extract/prepare/submit split) and raises the H1 gate — see phase-specs-expansion.md §B. Total P5 issues = 7.

Phase 5 — Parallelism & Determinism (W3) — concurrent with Phases 6, 7

Goal: Multicore engine loop; determinism guarantees Throne Phase 1 requires. 6 issues.

Batch 5.1 — Send + schedule (serial)

ID	Title	Grp	Effort	Blocked by
ENG2-P5-01	Make World/GoudContext Send; eliminate remaining global-static blockers	—	L	Phase 4 gate
ENG2-P5-02	Route the runtime loop through the existing ParallelSystemStage	—	M	P5-01

P5-01: context.rs:22 documents not-Send; all contexts behind one global Mutex (registry.rs:346); Phase 3 removed the component-store blockers — finish the job (thread-local window/immediate state maps at window/state.rs:361, immediate.rs:367).
P5-02: A working parallel scheduler with access-conflict analysis exists (schedule/parallel/execution.rs:85 rayon::scope) but App::run_once drives sequential SystemStage (ecs/app/mod.rs:163-165). Wire it; feature-flag for fallback during rollout.

Batch 5.2 — Jobs, determinism, pacing (3 groups, parallel)

ID	Title	Grp	Effort	Blocked by
ENG2-P5-03	Work-stealing job system for engine-internal work (propagation, culling, batch bake)	A	L	P5-01
ENG2-P5-04	Deterministic iteration order + world-state hash FFI hook	B	M	—
ENG2-P5-05	Frame pacing: target-FPS limiter without vsync + fixed-timestep render interpolation	C	M	—

P5-03: Replaces Throne’s Parallel.For stub (throne engine-dependencies.md:17); deterministic scheduling required (Throne phase-1.md:229).
P5-04: Throne Phase 1 gate needs same-seed identical state after 10k ticks across thread schedules (phases/phase-1.md:224-229); expose goud_world_state_hash so the consumer’s determinism test can compare runs.
P5-05: No frame limiter exists (pacing is wgpu present_mode only, init.rs:73-76); physics_world/interpolation.rs is a 26-LOC stub despite the real accumulator loop in sdk/game/instance_fixed_timestep.rs:37-48.

Batch 5.3 — Scale validation (serial)

ID	Title	Grp	Effort	Blocked by
ENG2-P5-06	H1 headless validation: 100k/1M published tick times, spawn/despawn soak, determinism CI job	—	M	P5-02..04

Phase 5 Gate

H1: 100k entities headless tick ≤ 5 ms; 1M ≤ 33 ms avg / 50 ms max; report committed.
Determinism: 3 seeds × 10k ticks ⇒ identical world hash, parallel stage ON, CI-gated.
Parallel propagation+culling ≥ 2.5× speedup on 8 cores vs single thread (bench).
Frame limiter holds 60 ± 1 FPS on S1 with vsync off.

══ SYNC B (throne_ge): THR-B-01 [M] — replace the Parallel.For/job stubs with the engine job system; wire goud_world_state_hash into DeterminismTests; re-run Throne Phase 1 scale gates against engine primitives.