agent: builder model: opus max_turns: 80 budget_usd: 16 —
?? result moves out of the element (E0507)Blocks: bt-build-time.md (step 5, known_default in crates/nikaia/src/comptime_run.rs:642, stays Rust until this is on develop)
Score: compiler bug, false acceptance (nikaia check passes, rustc refuses), and it blocks a self-hosting move (BT step 5); a Blocks: brief goes first in the bug lane (docs/architect.md, Lanes). One cause traced.
Facts: Where things live, Traps already met, Commands
A ?? with a jump fallback whose left side is an optional field (a type that does not copy) read off another ?? result - a list or map element - passes nikaia check and lowers to a match that moves the field out of the element: rustc refuses it (E0507 cannot move out of a shared reference). With the inner step bound by its own let, the same code runs (match c.signature.as_ref()).
use std::collections
struct Sig { name: String }
struct Con { signature: Sig? }
fn first(m: collections::BTreeMap[String, Con], key: String) -> String? {
let sig = (m.get(key) ?? return null).signature ?? return null
sig.name.clone()
}
fn main() {
let mut m: collections::BTreeMap[String, Con] = collections::BTreeMap()
m.insert("k", Con { signature: Sig { name: "one" } })
println(first(m, "k") ?? "none")
}Lowered: let sig = match match m.get(..) { Some(v) => v, None => return None }.signature { Some(v) => v, None => return None }; (want .signature.as_ref()).
Rows (probed on the fast binary at 0329f310):
one).fn first(xs: Vec[Con]) -> String? with let sig = (xs.get(0) ?? return null).signature ?? return null - E0507 (must print one, then none for []).(((m.get(key) ?? return null).signature ?? return null).config.get(at) ?? return null).default with Sig { config: Vec[Slot] }, Slot { default: String } - E0507 (must run).let c = m.get(key) ?? return null then let sig = c.signature ?? return null.(m.get(key) ?? return null).label ?? return null with label: String?.check_core_ops_coalesce, crates/nikaia-std/src/tools/check_core_ops.nika:752: the branch at :802 (A loan on the left and a jump on the right is a view, ADR-279 D10) records state.facts.lent_coalesces (.as_ref(), .as_deref() for text) only when the left side is check_core_ops_lent_root (:586) or check_core_ops_behind_a_view (:598).check_core_ops_behind_a_view walks Expr::Field bases through check_core_ops_place_type (:612), which knows names and field chains only: for a base that is an Expr::Coalesce it returns null, so the outer ?? is not lent and the emitter writes a moving match.emit_core_coalesce (emit_core_flow.nika:702) writes the opened form (emit_flow_opened, :696) from lent_coalesces.?? whose answer is a view of a list or map element counts as behind a view. The inner ?? has been checked first (check_core_expr on value, :757); its node is in state.facts.map_read_views (map read past a jump, :781) or lent_coalesces, or its left type is a view: pick the fact that holds for rows a, b and c, and say which in Body:. Why row e (text) already runs: probably the #735 branch at :812 or the text tiers; leave it.crates/nikaia-std/src/tools/lowered/check_core_ops.rs, regenerated by lower-std.Tests: (a-c E0507, d and e run).tests/compiler/tests/a_field_of_a_coalesce_is_read_through_a_view.nika + .stdout: rows a, b (both calls), c (a main that prints its answer for a present and an absent key), d and e, one function each. Commit check: an optional field read off a ?? result is a view of the element (Fixes #1055).The new test passes through nikaia test --project tests/compiler --both-settings and fails on the unfixed compiler; the tests nikaia run scripts/where.nika -- check_core_ops_coalesce check_core_ops_behind_a_view names pass (crates/nikaia/tests/it/ ones by filter, singly); the tests/compiler tests whose names contain coalesce pass; lower-std fixpoint clean (only lowered/check_core_ops.rs changes); cargo build --profile fast -p nikaia; 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_ops.nika, its lowered twin, files lower-std rewrites because of your change, and the test; an error in another agent’s file. tests/compiler failures from a binary vanishing mid-run (another agent rebuilding) are not yours: run the named tests singly.
Not yours, never stage: every file git status shows modified or untracked at your start (today among them crates/nikaia-std/src/tools/check_core_{flow,leaves,stmt}.nika, check_takes.nika and their lowered twins, crates/rs2nika/convert/*, docs/specification/30-nikaia-tooling.md), 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/b9-1055-field-of-a-coalesce.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