feat(igla): Wave Loop 897 — module-scope [613][2]^6 Pt non-power-of-two outer-dimension array-of-struct variable from call with indexed signed writes #1857

Next mechanical rung of the packed-vector array-of-struct ladder.

• Variant A: module-scope [613][2]^6 Pt variable initialized from a pure make_grid(0) call, with indexed signed field writes and assert_eq read-back inside a bench block.
• Expected: 39,232 elements, 1,255,424-bit packed vector, ~1.198 MiBit.
• Continues the post-1-MiBit boundary stress test.
• Zero compiler / reference-model / FROZEN_HASH changes expected.

Refs the Wave Loop autopilot plan.

User Scenarios

• Given a module-scope variable of type [613][2]^6 Pt (39,232 elements, 1,255,424-bit packed vector) initialized from a pure make_grid(0) call, When the bench block performs indexed signed field writes followed by assert_eq read-back, Then the packed-vector layout and signed-field semantics match the reference model exactly.

Requirements

• FR-001: The compiler MUST accept a module-scope [613][2]^6 Pt array-of-struct variable with non-power-of-two outer dimension (613).
• FR-002: The initializer make_grid(0) MUST produce a valid packed-vector constant for the given type at module scope.
• FR-003: Indexed signed field writes inside a bench block MUST correctly update the packed vector without compiler or reference-model changes.
• FR-004: The assert_eq read-back MUST verify bit-exact equality against the expected post-write state.
• FR-005: The test MUST pass with zero changes to the compiler, reference model, or FROZEN_HASH.

Success Criteria

• t27c specs/tri/collections/array.t27 exits with exit 0
• t27c specs/tools/trinity/tri/bench.t27 exits with exit 0
• python3 cli/t27b/bench/bench.py specs/tri/collections/array.t27 exits with exit 0 and reports 39,232 elements, 1,255,424-bit packed vector
• 5 tests pass in the Wave Loop 897 variant A test group

Boundary

• specs/tri/collections/array.t27
• specs/tools/trinity/tri/bench.t27
• specs/memory/graph/scope.t27
• cli/t27b/bench/bench.py