agent: builder model: opus max_turns: 80 budget_usd: 16 —
T? part at a match/if end is not wrapped in SomeBlocks: p5c-project-drive.md
Score: compiler bug, a lowering rustc refuses for a form the checker accepts. It blocks the P5c move (project_drive.nika: return match built.binary { null => (101, null), binary => (host.run_directly(binary), binary.clone()) }; the draft is on wip/p5c-project-drive cc40334f). Location traced by reading, fairly sure.
Facts: Where things live, Traps already met, Commands
A tuple with a T? part at an end of a match or if does not get Some on that part. This holds for a tail, a return and a let with a declared type. rustc refuses it: E0308, “Try wrapping the expression in Some”. The same tuple written directly, return (2, t.clone()), works.
Probe, row a (checked by the architect on 2026-10-31 19:45’s target/fast/nikaia, nikaia run):
fn pick(x: String?) -> (i32, String?) {
return match x {
null => (1, null),
s => (2, s.clone()),
}
}
fn main() {
let (a, b) = pick("x")
print(a)
print(b ?? "none")
}Expected 2x. Each of these fails the same way (all checked): row b is return if x { (2, t.clone()) } else { (1, null) } with x: bool, t: String. Row c is match x { 0 => (1, null), else => (2, t.clone()) } with x: i32. Row d is let r: (i32, String?) = match x { .. } followed by return r. Row e, the same match as a tail without return, takes the same path (check_function_wrap_tail). These already work and must keep working: if x { return (2, t.clone()) } then return (1, null), and a bare String? arm (s => s.clone() under -> String?).
crates/nikaia-std/src/tools/check_overflow.nika, check_overflow_list_into_nullables (called from check_widened_slot, the same file, which the tail, return, let and field paths all reach). It hands only a bare Expr::Tuple to check_overflow_tuple_into_nullables. An if/match/block falls to else => return false, so no part gets FactWrap::Constructor in state.facts.wrapped. Another catch: the found type for the whole match is the join of its ends, (i32, String?). Checked against that, the part s.clone() already looks nullable (!check_overflow_a_nullable(had) fails). Each end has to be compared with its own type. check_texts.nika tuple_literal already walks the ends (ends_in_tuple, tuple_ends, check_texts.nika :513, :531) and is the model. How each end’s own type is reached (a recorded type by node_key, or the end re-typed) is your choice: name it in Body:.
Tests:.tuple_ends are all tuple literals or null wraps each tuple end part by part, against that end’s own type. Any lowering rustc accepts. Name in Body: every function that repeats the rule (at least check_overflow_tuple_into_nullables, tuple_literal).lower-std and its fixpoint.tests/compiler/tests/tuple_option_part_in_arms.nika + .stdout with rows a-e and the two working forms, failing on the unfixed binary.
Commit check: a tuple at a match or if end wraps its optional parts (Fixes #1088).The new test fails on the unfixed compiler and passes through nikaia test --project tests/compiler --both-settings, together with the tests whose names contain tuple, nullable, option, optional, tail, widen (by name). Also: lower-std fixpoint clean; 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_overflow.nika, check_texts.nika, check_function.nika, their lowered twins and the new test, or you hit 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/b20-1088-tuple-option-part-in-arms.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