feat(igla): Wave Loop 818 — module-scope [455][2]^6 Pt non-power-of-two outer-dimension array-of-struct variable from call with indexed signed writes

Closes #1564

Author: Dmitrii Vasilev

.claude/plans/wave-loop-819.md

@@ -0,0 +1,45 @@
+# Wave Loop 819 Plan
+
+**Date:** 2026-07-29  
+**Issue:** #1565  
+**Branch:** `wave-loop-819`
+
+## Goal
+Continue the mechanical module-scope packed array-of-struct ladder from `[455][2]^6 Pt` to the next rung, choosing among three cooperation variants.
+
+## Variants
+
+### A — `[457][2]^6 Pt` module-scope packed array-of-struct variable from call with indexed signed writes (recommended)
+
+- Outer dimension increases by 2 to 457; inner dimensions stay `[2]^6`.
+- Expected witness: 29,184 elements, 933,888-bit packed vector (~0.891 MiBit).
+- Keeps the established mechanical generator pattern unchanged.
+- Generator `scripts/gen_w819.py` with `OUTER = 457`, `MID_IDX = 228`; fix copy hazard before first run.
+- Witness `specs/scratch/w819_bench_module_457x2p6_aos_var_call_write.t27`.
+- Add integration test `accepts_w819_bench_module_457x2p6_aos_var_call_write`.
+- Expected zero compiler / reference-model / FROZEN_HASH changes.
+
+### B — `[455][3]^6 Pt` — grow the second inner dimension to stress stride scaling
+
+- Keep outer dimension 455; change inner shape from `[2]^6` to `[3]^6`.
+- This exercises a different stride scaling direction: inner dimension 3 produces a 3^6 = 729 inner product, yielding 455 × 729 = 331,695 elements and 10,614,240 bits (~10.12 MiBit), which crosses the 4-MiBit cliff. Use only if the maintainers explicitly want to probe that boundary; otherwise it is intentionally more disruptive.
+
+### C — `[455][2]^6 Pt` with negative-index writes to exercise wrap-around addressing
+
+- Same outer/inner dimensions as variant A (455) but add negative signed index writes inside the bench block (e.g., `dst[-1][...] = ...`).
+- Verifies that the Verilog backend handles signed index wrap-around correctly.
+- Requires careful choice of negative indices so the wrapped positions are deterministic and the reference model agrees.
+
+## Recommended variant
+
+**A** — the mechanical ladder is still well below the 4-MiBit cliff at `[457][2]^6 Pt` (~0.891 MiBit), and the generator/test/seal pipeline is fully reusable. Variant A minimizes risk and keeps the ladder moving predictably.
+
+## Acceptance criteria
+
+- [ ] Generator `scripts/gen_w819.py` with `OUTER = 457`, `MID_IDX = 228`; copy hazard fixed before first run.
+- [ ] Witness `specs/scratch/w819_bench_module_457x2p6_aos_var_call_write.t27` generated and parsed.
+- [ ] `t27c icarus-lowerable`, `icarus-simulate`, `icarus-cocotb`, and `seal --save` all PASS.
+- [ ] Integration test `accepts_w819_bench_module_457x2p6_aos_var_call_write` added to `bootstrap/tests/icarus_lowerable.rs`.
+- [ ] `bootstrap/stage0/FROZEN_HASH` unchanged.
+- [ ] Closeout report, W820 cooperation plan, docs, skill tracker, autopilot skill, and persistent memory updated.
+- [ ] Commit with `Closes #1565`, push branch, open PR to `master`.

.claude/skills/t27-wave-loop.md

@@ -2390,6 +2390,48 @@ both. Continue grepping for stale wave numbers and outer dimensions after each
 copy, keep the `make_grid(32768)` period-identity check, and use `assert_eq` on
 changed elements because `assert_ne` is not emitted by the Icarus simulation path.
 
+## Worked example — Wave Loop 818
+
+Wave Loop 818 extended the module-scope packed-array-of-struct ladder with no
+compiler changes, branching from `wave-loop-817` HEAD because earlier wave PRs
+remained open awaiting review:
+
+- Generated `scripts/gen_w818.py` from `scripts/gen_w817.py` with `OUTER = 455`
+  and `MID_IDX = 227`.
+- Fixed both the generator destination path and the module header f-string from
+  stale `w817` / `453` references to `w818_bench_module_455x2p6_aos_var_call_write`
+  before regenerating; also corrected the stale `MID_IDX` comment to `227`.
+- Produced `specs/scratch/w818_bench_module_455x2p6_aos_var_call_write.t27`
+  (29,120 elements, 931,840-bit packed vector, ~0.889 MiBit).
+- Added integration test `accepts_w818_bench_module_455x2p6_aos_var_call_write`
+  after the existing W817 tests in `bootstrap/tests/icarus_lowerable.rs`.
+- Ran `t27c parse`, `icarus-lowerable`, `icarus-simulate` (17 cycles, PASSED),
+  `icarus-cocotb` (reference-model OK), and `t27c seal --save`.
+- No changes to `bootstrap/src/compiler.rs`, `bootstrap/stage0/FROZEN_HASH`, or
+  `scripts/cocotb_ref_model.py` for the witness itself.
+- Validation: `cargo build --release -p t27c` green,
+  `cargo clippy -p t27c` green (626 warnings, 0 errors),
+  `cargo test -p t27c --bin t27c` 1494/0/2, `cargo test -p tri` 78/0,
+  `cargo test -p flash-spi` 2/0,
+  `cargo test -p t27c --test bitnet_pipeline` 20/0,
+  `cargo test -p t27c --test bitnet_top` 17/0,
+  `cargo test -p t27c --test icarus_lowerable` 278/0,
+  `cargo test -p t27c --test verilog_const_array` 2/0.
+- Refreshed weak-point audit and 2025–2026 ternary/MVL literature scan.
+- Wrote `docs/reports/FPGA_LOOP_CLOSEOUT_W818_2026-07-29.md` and
+  `.claude/plans/wave-loop-819.md` with three cooperation variants.
+- Updated `.claude/skills/wave-loop-autopilot.md` run-list and status.
+- Updated this skill's Live Wave Loop Tracker to wave 819.
+
+Key learning: the mechanical ladder is now 45 waves deep (W774–W818) with zero
+compiler changes, confirming the packed-vector AoS lowering is robust up to at
+least `[455][2]^6 Pt` (29,120 elements, ~0.889 MiBit). The generator copy hazard
+remains the only manual failure mode and continues to span two text locations.
+A parameterized wave-prefix variable in the generator template would eliminate
+both. Continue grepping for stale wave numbers and outer dimensions after each
+copy, keep the `make_grid(32768)` period-identity check, and use `assert_eq` on
+changed elements because `assert_ne` is not emitted by the Icarus simulation path.
+
 ## Live Wave Loop Tracker
 
 This section is updated at the end of every completed Wave Loop. It is the
@@ -2398,13 +2440,13 @@ variants are queued."
 
 | Field | Value |
 |-------|-------|
-| **Current wave** | 818 |
-| **Issue** | #1564 (to open) |
-| **Branch** | `wave-loop-818` |
-| **Parent branch** | `wave-loop-817` HEAD because earlier wave PRs remain open |
-| **Recommended variant** | A — module-scope `[455][2]^6 Pt` packed array-of-struct variable from call with indexed signed writes |
+| **Current wave** | 819 |
+| **Issue** | #1565 |
+| **Branch** | `wave-loop-819` |
+| **Parent branch** | `wave-loop-818` HEAD because earlier wave PRs remain open |
+| **Recommended variant** | A — module-scope `[457][2]^6 Pt` packed array-of-struct variable from call with indexed signed writes |
 | **Status** | READY TO START |
-| **Next wave variants queued** | W819 Variant A `[457][2]^6 Pt`; Variant B `[455][3]^6 Pt` stride scaling; Variant C `[455][2]^6 Pt` negative-index wrap-around |
+| **Next wave variants queued** | W820 Variant A `[459][2]^6 Pt`; Variant B `[457][3]^6 Pt` stride scaling; Variant C `[457][2]^6 Pt` negative-index wrap-around |
 
 ### Open backlog (non-blocking)
 

.claude/skills/wave-loop-autopilot.md

@@ -62,10 +62,10 @@ criteria, generator copy-hazard checklist, and open backlog.
 | 815 | #1559 | wave-loop-815 | 449 | 224 | 28,736 | 919,552 | 0.877 | closed | TBD |
 | 816 | #1561 | wave-loop-816 | 451 | 225 | 28,864 | 923,648 | 0.881 | closed | #1560 |
 | 817 | #1562 | wave-loop-817 | 453 | 226 | 28,992 | 927,744 | 0.885 | closed | #1563 |
-| **818** | **#1564** | **wave-loop-818** | **455** | **227** | **29,120** | **931,840** | **0.889** | **READY** | **TBD** |
-| 819 | #1566 | wave-loop-819 | 457 | 228 | 29,248 | 935,936 | 0.893 | planned | TBD |
-| 820 | #1568 | wave-loop-820 | 459 | 229 | 29,376 | 940,032 | 0.897 | planned | TBD |
-| 821 | #1570 | wave-loop-821 | 461 | 230 | 29,504 | 944,128 | 0.900 | planned | TBD |
+| 818 | #1564 | wave-loop-818 | 455 | 227 | 29,120 | 931,840 | 0.889 | closed | #1566 |
+| **819** | **#1565** | **wave-loop-819** | **457** | **228** | **29,248** | **935,936** | **0.893** | **READY** | **TBD** |
+| 820 | #1567 | wave-loop-820 | 459 | 229 | 29,376 | 940,032 | 0.897 | planned | TBD |
+| 821 | #1569 | wave-loop-821 | 461 | 230 | 29,504 | 944,128 | 0.900 | planned | TBD |
 
 ### Run-list notes
 - Issue numbers follow the observed pattern (issue = previous issue + 2; PR = issue + 1).
@@ -152,10 +152,10 @@ criteria, generator copy-hazard checklist, and open backlog.
 
 ## Current status
 
-- **Latest completed wave:** 817
-- **Latest issue/PR:** #1562 / #1563
-- **Current wave in progress:** 818
-- **Next wave queued:** 819
-- **Ladder depth:** W774–W817 = 45 waves
+- **Latest completed wave:** 818
+- **Latest issue/PR:** #1564 / #1566
+- **Current wave in progress:** 819
+- **Next wave queued:** 820
+- **Ladder depth:** W774–W818 = 45 waves
 
 *φ² + φ⁻² = 3 | TRINITY*

.trinity/current-issue.md

@@ -1,28 +1,28 @@
-# Current Issue — Wave Loop 818
+# Current Issue — Wave Loop 819
 
 | Field | Value |
 |-------|-------|
-| Wave | 818 |
-| Issue | #1564 |
-| Branch | `wave-loop-818` |
-| Base | `wave-loop-817` (parent branch because earlier waves' PRs remain open) |
-| Variant | `[455][2]^6 Pt` module-scope AoS variable from call with indexed signed writes |
-| Target packed vector | 29,120 elements × 32 bits = 931,840 bits (~0.889 MiBit) |
+| Wave | 819 |
+| Issue | #1565 |
+| Branch | `wave-loop-819` |
+| Base | `wave-loop-818` (parent branch because earlier waves' PRs remain open) |
+| Variant | `[457][2]^6 Pt` module-scope AoS variable from call with indexed signed writes |
+| Target packed vector | 29,184 elements × 32 bits = 933,888 bits (~0.891 MiBit) |
 | Status | planned |
 
 ## Goal
-Increment the non-power-of-two outer-dimension ladder by one rung to `[455][2]^6 Pt`, keeping the established inner-dimension (`2^6`) and struct (`Pt { x : i16, y : i16 }`) pattern. Validate that t27c still lowers, simulates, cocotb-matches, and seals the wider packed vector without compiler or FROZEN_HASH changes.
+Increment the non-power-of-two outer-dimension ladder by one rung to `[457][2]^6 Pt`, keeping the established inner-dimension (`2^6`) and struct (`Pt { x : i16, y : i16 }`) pattern. Validate that t27c still lowers, simulates, cocotb-matches, and seals the wider packed vector without compiler or FROZEN_HASH changes.
 
 ## Acceptance criteria
-- [ ] Generator `scripts/gen_w818.py` with `OUTER = 455`, `MID_IDX = 227`; copy hazard fixed before first run.
-- [ ] Witness `specs/scratch/w818_bench_module_455x2p6_aos_var_call_write.t27` generated and parsed.
+- [ ] Generator `scripts/gen_w819.py` with `OUTER = 457`, `MID_IDX = 228`; copy hazard fixed before first run.
+- [ ] Witness `specs/scratch/w819_bench_module_457x2p6_aos_var_call_write.t27` generated and parsed.
 - [ ] `t27c icarus-lowerable`, `icarus-simulate`, `icarus-cocotb`, and `seal --save` all PASS.
-- [ ] Integration test `accepts_w818_bench_module_455x2p6_aos_var_call_write` added to `bootstrap/tests/icarus_lowerable.rs`.
+- [ ] Integration test `accepts_w819_bench_module_457x2p6_aos_var_call_write` added to `bootstrap/tests/icarus_lowerable.rs`.
 - [ ] `bootstrap/stage0/FROZEN_HASH` unchanged.
 - [ ] Closeout report, next-wave plan, docs, skill tracker, autopilot skill, and persistent memory updated.
-- [ ] Commit with `Closes #1564`, push branch, open PR to `master`.
+- [ ] Commit with `Closes #1565`, push branch, open PR to `master`.
 
-## Cooperation variants for W819
-- **A (recommended):** `[457][2]^6 Pt`, outer += 2, MID_IDX = 228.
-- **B:** `[455][3]^6 Pt` — grow the second inner dimension to stress stride scaling.
-- **C:** `[455][2]^6 Pt` with negative-index writes to exercise wrap-around addressing.
+## Cooperation variants for W820
+- **A (recommended):** `[459][2]^6 Pt`, outer += 2, MID_IDX = 229.
+- **B:** `[457][3]^6 Pt` — grow the second inner dimension to stress stride scaling.
+- **C:** `[457][2]^6 Pt` with negative-index writes to exercise wrap-around addressing.

.trinity/current_task/activity.md

@@ -3956,3 +3956,7 @@
 - **Commit:** feat(igla): Wave Loop 817 — module-scope [453][2]^6 Pt non-power-of-two outer-dimension array-of-struct variable from call with indexed signed writes
 - **Files:** .claude/skills/wave-loop-autopilot.md,docs/NOW.md,docs/reports/FPGA_LOOP_CLOSEOUT_W817_2026-07-29.md
 
+## 2026-07-30T04:45:45Z — wave-loop-818
+- **Commit:** docs: record W817 PR #1563 in NOW.md, autopilot skill, and closeout report
+- **Files:** .claude/plans/wave-loop-819.md,.claude/skills/t27-wave-loop.md,.claude/skills/wave-loop-autopilot.md,.trinity/current-issue.md,.trinity/experience.md,.trinity/seals/scratch_w818_bench_module_455x2p6_aos_var_call_write.json,bootstrap/tests/icarus_lowerable.rs,docs/NOW.md,docs/reports/FPGA_LOOP_CLOSEOUT_W818_2026-07-29.md,scripts/gen_w818.py,specs/scratch/w818_bench_module_455x2p6_aos_var_call_write.t27
+

.trinity/experience.md

@@ -1,3 +1,67 @@
+## 2026-07-29 — Wave Loop 818 (module-scope `[455][2]^6 Pt` non-power-of-two outer-dimension AoS variable, issue #1564)
+
+### What worked
+- Variant A extended the module-scope packed AoS odd outer-dimension ladder to 455.
+  The `[455][2]^6 Pt` witness is 931,840 bits (~0.889 MiBit), still well under the 4-MiBit
+  cliff, and required no compiler changes.
+- A module-level `pub var dst : [455][2]^6 Pt` can be initialized from a function
+  call and exercised with indexed signed field writes, with zero compiler changes.
+- The cocotb/Python reference model correctly mirrored the row-major flattening
+  with outer stride 455, confirming the layout is preserved end-to-end.
+- Reused the corrected W632 element-index formula for mid-row expected values:
+  `[r][a5][a4][a3][a2][a1][a0]` is element `r*64 + a5*32 + a4*16 + a3*8 + a2*4 + a1*2 + a0`.
+- For `OUTER = 455`, `MID_IDX = 227`; the frame-condition element is
+  `[227][1][0][0][0][0][0]`, element number `227*64 + 32 = 14,560`.
+- The generator copy hazard struck again after copying `scripts/gen_w817.py` →
+  `scripts/gen_w818.py`. Both the destination path and the module header f-string
+  carried stale `w817` / `453` references. Fixing both before regenerating resolved it.
+  The stale `MID_IDX` comment was also corrected to `227`.
+  This is the same hazard documented in W782–W817 learnings and remains the only
+  manual step in the otherwise mechanical flow.
+- Fresh weak-point audit (2026-07-29) found no new actionable items. The W783 fix
+  for `bootstrap/tests/verilog_const_array.rs:166` remains green; the pre-existing
+  `verilog_array_literal_expr` regression is still out of scope for the witness ladder.
+- 30-day subject-line traceability remained low; the closeout commit carries
+  `Closes #1564` in the subject, but the overall rate needs improvement.
+  Continue putting issue references in commit subjects.
+- Updated the live Wave Loop Tracker in `.claude/skills/t27-wave-loop.md` to wave 819.
+- Updated `.claude/skills/wave-loop-autopilot.md` to mark W818 READY, W819 planned,
+  and refreshed the master run-list.
+
+### What changed behavior
+- No changes to `bootstrap/src/compiler.rs`.
+- No changes to `bootstrap/stage0/FROZEN_HASH` (`68a0b933c00ba5efd7facb5997f00880c3eecae55e6ac5e8cea2aee399b92adc`).
+- No changes to `scripts/cocotb_ref_model.py`.
+- Added `specs/scratch/w818_bench_module_455x2p6_aos_var_call_write.t27` (~1,998 KB /
+  ~86,511 lines) with seal and Icarus baseline.
+- Added integration test `accepts_w818_bench_module_455x2p6_aos_var_call_write`
+  in `bootstrap/tests/icarus_lowerable.rs`.
+- Added generator script `scripts/gen_w818.py`.
+- Wrote `docs/reports/FPGA_LOOP_CLOSEOUT_W818_2026-07-29.md` and
+  `.claude/plans/wave-loop-819.md` with three cooperation variants.
+- Updated `.claude/skills/t27-wave-loop.md` live tracker to wave 819.
+
+### Validation
+- `cargo build --release -p t27c`: OK.
+- `cargo clippy -p t27c`: OK (626 warnings, 0 errors).
+- `cargo test -p t27c --bin t27c`: 1494 passed; 0 failed; 2 ignored.
+- `cargo test -p tri`: 78 passed; 0 failed.
+- `cargo test -p flash-spi`: 2 passed; 0 failed.
+- `cargo test -p t27c --test bitnet_pipeline`: 20 passed; 0 failed.
+- `cargo test -p t27c --test bitnet_top`: 17 passed; 0 failed.
+- `cargo test -p t27c --test icarus_lowerable`: 278 passed; 0 failed.
+- `cargo test -p t27c --test verilog_const_array`: 2 passed; 0 failed.
+- Direct `t27c parse` W818: PASS.
+- Direct `t27c icarus-lowerable` W818: PASS (`lowerable`).
+- Direct `t27c icarus-simulate` W818: PASS (17 cycles, PASSED).
+- Direct `t27c icarus-cocotb` W818: PASS (`reference-model OK`).
+- Direct `t27c seal --save` W818: PASS.
+
+### Scientific / engineering background
+- IEEE 1800-2017 §7.4.1/7.4.3 define packed-array width as the product of packed
+  dimensions, with no power-of-two restriction. Variant A emits a single
+  931,840-bit packed vector, which is legal SystemVerilog.
+
 ## 2026-07-29 — Wave Loop 817 (module-scope `[453][2]^6 Pt` non-power-of-two outer-dimension AoS variable, issue #1562)
 
 ### What worked

.trinity/seals/scratch_w818_bench_module_455x2p6_aos_var_call_write.json

@@ -0,0 +1,11 @@
+{
+  "gen_hash_c": "sha256:b54f4e4545743b5731fb2f72e310536cc8154fed82769a52ce06524275df5908",
+  "gen_hash_rust": "sha256:8a53e15a700cd6df46cfbe48101011b6e1a842d71309b6ba75a1fd7a684990c3",
+  "gen_hash_verilog": "sha256:0b56e889386a13aee4aced999ecbb676a94b7cfee4acf4eae95117d0c8478848",
+  "gen_hash_zig": "sha256:8461dff93d83f405a8041ac49faadf0b76428c32f58625e74dbbd6712adce676",
+  "module": "w818_bench_module_455x2p6_aos_var_call_write",
+  "ring": 12,
+  "sealed_at": "2026-07-30T03:08:11Z",
+  "spec_hash": "sha256:a907723555069e7a3b3260b73842f3f8f72d52ea19d71d0ac6f7833bd434a149",
+  "spec_path": "/Users/playra/t27/specs/scratch/w818_bench_module_455x2p6_aos_var_call_write.t27"
+}

bootstrap/tests/icarus_lowerable.rs

@@ -5017,6 +5017,24 @@ fn accepts_w817_bench_module_453x2p6_aos_var_call_write() {
     }
 }
 
+#[test]
+fn accepts_w818_bench_module_455x2p6_aos_var_call_write() {
+    let dir = scratch_dir();
+    for name in &[
+        "w818_bench_module_455x2p6_aos_var_call_write.t27",
+    ] {
+        let p = dir.join(name);
+        assert!(p.exists(), "missing W818 witness {}", p.display());
+        let (lowerable, json) = run_icarus_lowerable(&p);
+        assert!(
+            lowerable,
+            "expected {} to be lowerable, got: {}",
+            p.display(),
+            json
+        );
+    }
+}
+
 #[test]
 fn accepts_known_lowerable_witnesses() {
     let dir = scratch_dir();