agent: builder model: opus max_turns: 80 budget_usd: 16 —
Score: compiler bug, false acceptance (nikaia check passes, rustc refuses E0507); found by b8 (#1044) on the same code path; one cause traced, small and certain. Runs after b9 (#1055) in this batch, in another file.
Facts: Where things live, Traps already met, Commands
A field that does not copy, read off a local bound to an element read and handed back by value, passes nikaia check and fails in rustc. The whole element is refused since #1044 (920d8608, NK1131, help …?.clone()); its field is not.
struct Inner { name: String }
struct Item { inner: Inner }
fn last_inner(path: Vec[Item]) -> Inner? {
let s = path.last() ?? return null
return s.inner
}
fn main() {
let xs = [Item { inner: Inner { name: "a" } }, Item { inner: Inner { name: "b" } }]
let r = last_inner(xs) ?? return
println(r.name)
}Rows:
s.inner which is behind a shared reference; want NK1131 naming s.inner and path, help Write `s.inner.clone()` for a copy.fn inner_of(m: collections::BTreeMap[String, Item], k: String) -> Inner? with let s = m.get(k) ?? return null then return s.inner - today the same rustc error; want NK1131 naming m.b, must stay): return s.inner.clone().return s - NK1131 (#1044).return (path.last() ?? return null).inner and let x = s.inner; return x.check_core_a_lent_place_given_away, crates/nikaia-std/src/tools/check_core_leaves.nika:117, the Expr::Field arm (:158): state.place_path gives s.inner, root s; then if root == "self" || !state.lent_here(root) { return } (:226) returns, because s is a let whose view_of is path.last(), not a lent parameter.state.binding(written), local.view_of, check_core_leaves_list_of_a_read(list) (:93) non-null, then check_core_leaves_an_element_read_given_away (:111).root is known and before :226, when keeps holds, state.binding(root) has a view_of that check_core_leaves_list_of_a_read reads as a list, and the field’s type (check_core_expr on value) does_not_copy, push NK1131. The message should say s.inner is part of an element path keeps; the help copies the field path: Write `s.inner.clone()` for a copy. (not ?.clone(): the field is not optional). Either give check_core_leaves_an_element_read_given_away a help parameter or write the refusal beside it; one rule, one place.crates/nikaia-std/src/tools/lowered/check_core_leaves.rs, regenerated by lower-std.Tests:.tests/compiler/tests/a_field_of_an_element_read_handed_back.nika + .stderr (rows a and map, one function each, two NK1131), tests/compiler/tests/a_field_of_an_element_read_copied.nika + .stdout (row d). If Part III’s NK1131 entry (docs/specification/30-nikaia-tooling.md) says element reads are refused whole only, add “or a field of one” there. Commit check: a field of an element read, handed back by value, is NK1131, with Part: #1057 (step 2 stays open).The refusal test fails on the unfixed compiler and passes through nikaia test --project tests/compiler --both-settings (by name); the existing tests an_element_read_handed_back_by_value and an_element_read_copied_with_clone pass; lower-std fixpoint clean (only lowered/check_core_leaves.rs changes, plus any tools/*.nika the new refusal now catches: such a hit is a real move out of an element, so stop and report it as Found:, do not rewrite it); build, fmt, clippy, pre-push-check.sh; committed locally. Changelog: one line. Stop about 15 turns before max_turns, commit what is finished and report partial.
An edit is needed outside check_core_leaves.nika, its lowered twin, Part III’s NK1131 entry and the tests; an error in another agent’s file.
Not yours, never stage: every file git status shows modified or untracked at your start, and every docs/briefs/* file except your report.
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 (scripts/commit.nika -- REPORT does it); commit locally after each step and never push: the driver runs the complete suite and pushes (.claude/agents/builder.md, Cheap checks only; owner, 2026-10-31).cargo build --profile fast -p nikaia, lower-std and its fixpoint when a tools/*.nika changed, cargo fmt, cargo clippy --all-targets -- -D warnings, scripts/pre-push-check.sh, the tests the brief names and the ones your change touches. No gate.nika.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: architect 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.Result: partial with what you ruled out, the probe, and the suspected file and function (.claude/agents/builder.md).target/fast/nikaia run scripts/commit.nika -- REPORT, which writes Pushed: local <sha> into it. 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/bugs/b10-1057-field-of-an-element-read.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