Phase 1 / Forge / forge_3d orchestration: PhysicsWorld and ECS Transform synchronisation

[guysenpai]

Brief

briefs/m1.1.15-physics-world-orchestration.md

DRAFT, opened at the first gate as engine-development-workflow.md §4.4 requires: ci.yml fires on pull_request and not on a branch push, so a gate whose exit depends on a matrix cell is unreachable until the PR exists. Gate A's exit is exactly that — the eight committed determinism witnesses byte-identical on the twelve-cell matrix, and the four CHAIN witnesses are x86_64 artifacts that no local corner can verify.

No Witness-regen: trailer appears anywhere in this branch, and none will. A red witness here is a defect to isolate, not an act to declare.

Summary

forge_3d had every mechanism the arena needs and no owner for the tick that runs them. This milestone creates that owner: PhysicsWorld executes the eleven steps of engine-physics-solver.md §1.7 in their frozen order, wires the pieces the body store cannot wire from inside, and connects the solver to the ECS in both directions.

Gate progress

Gate	State
A — PhysicsWorld and the tick	delivered, awaiting the matrix reading
B — proxies and body lifetime	pending
C — wake composition	pending
D — ECS synchronisation	pending
E — precision crossing, interface file, false premises	pending
F — closure	pending

Gate A — what landed

• The eleven-step cycle MOVED out of tests/solver_test.zig — where its only composition lived, driven by ten suites — into forge_3d/world.zig. Call sequence, arguments and arithmetic unchanged: the reparenting changes who calls, never what is computed.
• step() reads as the cycle: nine stage methods in order, plus the two code-free anchors as comments where they would run (3 read-only, 5 bis the empty composite seam of §1.7.3). Each stage method opens with its own enter(), which is what binds the recorded order to the executed one.
• Step 10 bis is now UNCONDITIONAL. The harness gated it on a sensors_on flag defaulting to false; in production that reads "sensors silently do not work". SensorState.update takes a *const BodyManager, so the pass cannot alter a bit of body state and the change is witness-neutral by construction.
• SolverStats.warm_start_injections — real injections, not loop turns. Documented as NOT part of what §1.8.2 reports; see the brief's Notes, and flagged there for your call.

Gate A — measurements

Determinism instrument, all four local corners green ({Debug, ReleaseSafe} × {f32, f64}, macOS aarch64): self-reproducible, the four discrete traces byte-identical to the committed witnesses, no divergence within K = 60. The four chain witnesses read REPORTED, not gated on this host because level 1 is intra-ISA — that is the matrix's half of the exit.

Counter-factuals, four RUN, and the fourth is a residual rather than a confirmation:

Probe	Mutation	Measured
A	swap the calls of stages 10 and 10 bis	1 failed of 561 — the order test, that adjacency's only guard
B	hoist the warm start out of the substep loop	cadence test: expected 16, found 4, plus 6 physics tests
D	swap the calls of stages 4 and 5	4 failed, 35 crashed — where order matters physically, dozens fire
C	swap two stage BODIES, leave each enter()	whole suite green — the residual, written into the code

Probe C is the honest limit: a record separated from its work is undetectable by any test here. What bounds it is structural — each enter() is the first statement of the stage method carrying its name — and that is a smaller claim than "the order is verified", stated as such in world.zig and in the test.

Counts, with their denominators. zig build test-forge-3d collects 561 on this branch (560 pass, 1 skip) against 555 on main at e02d27b, measured in a worktree, both macOS aarch64: +6, the six blocks added in tests/world_test.zig. Full suite 1875 collected. The dead-tests declared floor was re-derived from the SUITE (1875), never from the closure's own arithmetic.

One test assertion removed, declared in the brief's Recorded deviations: expect(s.world.sensors_on) in the determinism scenario had no flag left to read. It is replaced by two assertions obtained by different mechanisms — the scenario's trigger asserted on the body's ROLE, and the unconditional pass asserted on the STATE it produces, in tests/world_test.zig.

Local gates

• zig build clean
• zig build test — 1875 collected, 1856 pass, 19 skip
• zig build test-forge-3d — 561 collected, 560 pass, 1 skip
• zig fmt --check green over src/ tests/ bench/ tools/ build.zig
• zig build lint green, dead-tests conservation reconciled at 1875
• zig build forge-determinism green on the four local corners
• the twelve-cell matrix — this PR's reason for existing at Gate A