Wave Loop 777 — module-scope [373][2]^6 Pt non-power-of-two packed AoS variable with indexed signed writes

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Wave Loop 777 validates a module-scope [373][2]^6 Pt packed array-of-struct variable initialized from a function call, with indexed signed field writes and assert_eq read-back in a bench block.

This is the next step in the odd-outer-dimension ladder (339 → 341 → 343 → 349 → 351 → 353 → 355 → 357 → 359 → 361 → 363 → 365 → 367 → 369 → 371 → 373).

Acceptance criteria

• specs/scratch/w777_bench_module_373x2p6_aos_var_call_write.t27 is generated and parses.
• The witness is Icarus-lowerable and simulates correctly (17 cycles, PASSED).
• The cocotb reference model matches the t27 semantics.
• t27c seal --save succeeds and FROZEN_HASH remains unchanged.
• All cargo suites remain green.
• Integration test accepts_w777_bench_module_373x2p6_aos_var_call_write is added.
• Closeout report docs/reports/FPGA_LOOP_CLOSEOUT_W777_2026-07-24.md is written.
• Learning is saved to .trinity/experience.md, memory, .claude/skills/t27-wave-loop.md, and .trinity/current-issue.md.
• .claude/plans/wave-loop-778.md with three cooperation variants is created.

Technical notes

• Shape: [373][2]^6 Pt where Pt = pub struct Pt { x : i16, y : i16 }.
• Total elements: 373 x 64 = 23,872.
• Packed vector width: 23,872 x 32 = 764,416 bits (~0.729 MiBit).
• MID_IDX = 186; frame-condition element [186][1][0][0][0][0][0] is element 186*64 + 32 = 11,936.
• Generator script: scripts/gen_w777.py (copy from scripts/gen_w776.py, set OUTER = 373 and MID_IDX = 186, fix module prefix).
• Use assert_eq checks on changed elements (Icarus simulation path does not emit assert_ne).
• Include make_grid(32768) period-identity check because 32768 == 0 (mod 32768).
• Zero compiler / reference-model / FROZEN_HASH changes expected.