agent: builder model: opus max_turns: 100 budget_usd: 20 —
Score: compiler bug, a false acceptance (rows b, c: the checker passes, rustc refuses) and a false refusal (rows a, f: NK1245); bugs-first default of docs/priorities.md. Kind 3 (defect), not a decision: D34 makes a list’s literal elements one open number, and D43 extends it to a map’s values to keep “one rule for every place a number literal is stored”; a list of lists is that rule one level further.
Step 1 is built for one level (for n in [1, 2], a6ec14b3, test tests/compiler/tests/a_loop_over_an_untyped_number_list_copies.nika). Left: a list whose items are lists of numbers gets no open number, so its let gets no written type, rustc falls back to i32, and a use that asks for i64 fails in rustc (b938’s report, traced with a replica of num::value).
Probe matrix (architect, at dd9d5470; every program starts fn twice(n: i64) -> i64 { return n * 2 } where it calls twice, and fn main() { + let grid = [[1, 2], [3]]):
| Row | Body after the let | Today | Expected |
| :— | :— | :— | :— |
| a | println(f"{grid[0][1] + grid[1][0]}") | NK1245 “can’t tell what type grid[0][1] is” | 5 |
| b | for n in grid[0] { println(f"{twice(n)}") } | rustc Mismatched types | 2, 4 |
| c | for r in grid { for n in r { println(f"{twice(n)}") } } | rustc Mismatched types | 2, 4, 6 |
| d | let mut s = 0 / for r in grid { for n in r { s = s + n } } / println(f"{s}") | 6 | 6 (guard) |
| e | println(f"{total(grid)}") with fn total(xs: Vec[Vec[u8]]) -> u8 { return xs[0][0] + xs[1][0] } | 4 | 4 (guard: the parameter asks u8) |
| f | let cube = [[[1, 2]], [[3]]] / println(f"{cube[1][0][0] + 1}") | NK1245 | 4 |
| g | let row = grid[0] / let x: u8 = row[0] / println(f"{x}") | 1 | 1 (guard: row’s elements are the same number) |
Each of a, b, c with let grid: Vec[Vec[i64]] = ... prints the expected output today, so the written type is the whole cause. Traced to the missing open number: b, c (b938). a, f: NK1245 from open_numbers_in finding no open number for grid[0][1] (open_element_in takes only a Variable base); unverified beyond that. d, e, g run today only because no type is written; once one is, they hold only if the asks reach the number: they are the regression rows.
let: crates/nikaia-std/src/tools/check_core_stmt.nika:726-770 (Expr::ListLit whose items are all number_shaped opens the number, element_at; stored at :883 in state.flow.open_elements).for: same file :1556-1595 (a Variable walk reads open_elements, binds frame[0].open_number, and since a6ec14b3 records copied_loop_bindings). for r in grid must give r its elements’ number; for n in grid[0] must find it through the index.CheckOpenNumber in crates/nikaia-std/src/tools/check_flow.nika:26 (element: bool; open_elements :246); 5 struct literals of it (grep -n "CheckOpenNumber {"), the let’s is check_core_stmt_open_number (check_core_stmt.nika:335).crates/nikaia-std/src/tools/check_numbers3.nika:207-220 (written = f"Vec<{ty}>" for an element number, into facts.number_lets; the emitter writes it, no emitter change expected). Message at :104 and :136 (“the elements of grid”).crates/nikaia-std/src/tools/check_numbers4.nika open_element_of/open_element_in/open_element_named :146-170, open_numbers_in :205, elements_asked :479 (row e: Vec[Vec[u8]] must ask u8 of the inner number; number_list_element :401), open_items_of :744.open_elements: check_core_call_on.nika :375, :432, :558, :600-634 (method calls on an open list).let is fine)CheckOpenNumber gains the count of list levels around its numbers (0 for a name’s own number, 1 for [1, 2], 2 for [[1, 2], [3]]), and number_lets writes that many Vec<..>. A local whose items are lists of the number (grid) is recorded with the number and its level, so grid[i] and a for over grid hand the next level down (row, r get open_elements), and grid[i][j] is the number. A list literal of list literals opens one number only when every innermost item is number_shaped and every level is a list literal; anything else stays as today.
let, its written type, and the reads and asks above, so rows a-g give the expected column. One commit, with the new test tests/compiler/tests/a_list_of_number_lists_has_one_open_number.nika + .stdout holding rows a, b, c, e, f, g in one program (d is covered by them; keep its s loop in if it costs nothing). Check the test fails on the unfixed compiler.nikaia test --both-settings --project tests/compiler > out.txt 2>&1 once (no name filter exists; grep the file for the new test and a_loop_over_an_untyped_number_list_copies), the guard set of .claude/agents/builder.md, lower-std to fixpoint as docs/builder-facts.md says.Commit: check: a list of number lists has one open number for its innermost elements (Fixes #938).
max_turns: commit what is finished and report partial.check_core_stmt.nika, check_flow.nika, check_numbers3.nika, check_numbers4.nika, check_core_call_on.nika, their lowered/*.rs and the new test would have to change: report, do not change it.Result: blocked, Needs:.docs/builder-facts.md first. develop in the main checkout; git status at start: other agents’ uncommitted files are not yours, never touch or stage them.git add <files> only; commit after each step; git push origin develop fast-forward, no rebase (rejected: report Pushed: rejected, go on committing).cargo fmt, cargo clippy --all-targets -- -D warnings, scripts/pre-push-check.sh, and the gate of .claude/agents/builder.md (#852).CHANGELOG.md, badges; no new NK code. New tests in Nikaia only; never the full suite. No foreground sleep, no polling; scripts in files.std or the toolchain lacks stops the work: no code around it unless an ADR or Part I-III refuses it (name it). Else Result: blocked, Found: gap + probe, Needs: owner decision (CLAUDE.md, A missing form stops the work).NIKAIA_CACHE_LIMIT=2G; at most two clones with target/ in the machine; delete your own clone’s target/ and target/release/nikaia-scratch at the end; report GB freed.Pushed: line names the pushed sha. A report without a Pushed: line, or with a placeholder left in (TC, DISK), is not done and cuts the batch (k3a1 2026-10-29: Result: done, nothing committed)./home/user/Nikaia/docs/briefs/b938b-nested-number-lists.md.report.md)Fields of docs/architect.md, Briefs and reports: Result: done|noop|partial|blocked (the bare word alone on that line: Result: done, never a summary after it, which cuts the batch, b869a 2026-10-27; Owner: is a question for the owner or none, never a role), Files, Commit, Body (optional, one paragraph for the commit message), Fixes, Pushed, Tests, Gate (green|red), Deviation, Found, Needs, Changelog, Owner, Disk freed, and for a move Rs2nika: (the kept N of M lines of rs2nika --score, then the three costliest hand edits; none for a task that moves no Rust, none (redesign) for a brief with Shape: redesign and no Convert: line). none where nothing, and then the bare word: Deviation: none (a note) cuts the batch (batch.nika compares exactly); a note goes into the commit message. Found: is only for a defect outside your change (it cuts the batch); a process event such as another session resetting or rewriting your files is no Found:, it goes under Needs: (m3a 2026-10-28); a converter draft that came out wrong is no Found:, it is one of the costliest edits under Rs2nika:, which the converter lane reads (e12-4b 2026-10-27); how you solved your own step goes into the commit message. Deviation: is only a step of the brief built otherwise than written or not built (a choice the brief left to you, such as keep what X needs and say so, is no deviation: it goes into the commit message; nor is building two steps in one commit when every step is built, e12-3a 2026-10-27, nor a step another commit on develop already built, shown by your test failing with that commit’s change reverted, b889 2026-10-27: name the commit in Body:, nor a test’s expected .stdout/.stderr taken from what the program really prints where the brief’s sketch of it was short or wrong, b934 2026-10-29: say so in Body:, nor a lowering that follows the ADR governing it where the brief’s expected lowering contradicts that ADR, b933 2026-10-29: name the ADR in Body:, nor a lowering other than the brief’s where rustc cannot take the brief’s, b1029 2026-10-31: say why in Body:, nor re-keying an allow-list entry (KNOWN) whose hash changed for the same program and the same reason, b-fixforward-sweep2 2026-10-28: say so in Body:, nor an existing test’s expected .stdout/.stderr updated because your change rightly changes the message it prints, b1012b 2026-10-31: name the test in Body:); how you verified (e.g. a test not run against the unfixed compiler) goes under Tests:. A noop says why under Tests: (what was probed), not under Deviation:. Final answer, one line: done <sha>, report <path> (or BLOCKED: ... / PUSH REJECTED ...).
Attribution: Co-Authored-By: Claude Opus 5.5 noreply@anthropic.com Claude-Session: https://claude.ai/code/session_01GFeMqxRbtUMiGVyDMxsvEq