feat(igla): Wave Loop 894 — module-scope [607][2]^6 Pt non-power-of-two outer-dimension array-of-struct variable from call with indexed signed writes #1851

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

• Variant A: module-scope [607][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: 38,848 elements, 1,243,136-bit packed vector, ~1.186 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 [607][2]^6 Pt array-of-struct variable initialized from a pure make_grid(0) call, when indexed signed field writes are performed and read back with assert_eq inside a bench block, then the packed vector contains 38,848 elements totaling 1,243,136 bits (~1.186 MiBit).

Requirements

FR-001: The compiler MUST accept module-scope [607][2]^6 Pt variable declarations with make_grid(0) initialization.
FR-002: The compiler MUST support indexed signed field writes to the array-of-struct elements.
FR-003: The bench block MUST execute assert_eq read-back verification correctly.
FR-004: The resulting packed vector size MUST be 1,243,136 bits (38,848 elements).
FR-005: Zero changes to compiler, reference model, or FROZEN_HASH are required.

Success Criteria

• t27c specs/tools/trinity/tri/bench.t27 compiles and the bench block exits with exit 0
• The bench output reports 38,848 elements and 1,243,136-bit packed vector
• 1 test passes for Wave Loop 894 Variant A in specs/tools/trinity/tri/bench.t27

Boundary

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