agent: builder model: opus max_turns: 110 budget_usd: 22 —
Score: self-hosting lane (docs/priorities.md; #125, docs/selfhosting-plan.md C-7 rest and E12, row E12-4, the last E12 row; 79.1 % after E12-3b). E12-4 is split by the architect (2026-10-27): 4a (this) moves what needs no Default from the lowering; 4b moves Target and Build and needs a lowered impl Default from field defaults (ADR-331 D5) first.
crates/nikaia/src/emit/mod.rs: UserParallelism (:78, parse :386, is_concurrent, parallelism(self, target) :411), ReentrancyCheck (:103, parse :112, is_on). Both derive Debug, Clone, Copy, PartialEq, Eq, Default with #[default]. The lowering already derives Debug, Clone, Copy, PartialEq, Eq for a data-less enum (36 such in tools/lowered/), never Default.Default on the two enums is used only through Build’s #[derive(Default)] (:138) and one ReentrancyCheck::default() (grep it). So: replace Build’s derive by a hand impl Default for Build naming Target::default(), UserParallelism::No, ReentrancyCheck::Yes and the rest of its fields’ defaults (Build is Rust until 4b; this is no workaround), and the one call by ReentrancyCheck::Yes.crates/nikaia/src/emit/rust_targets.rs: RUST_TARGETS, a list of ~300 triples; its only reader is Target::parse-side code at emit/mod.rs:283 (Target::Rust(known) keeps the &'static str). Risk named in the plan: a list literal of ~300 strings in a tools file (lowering cost, not seen yet). If the lowered form cannot give a &'static str (for Target::Rust), expose emit_build_rust_target(triple: ref String) -> i64 (index or -1) plus a Rust &'static str view of the lowered list, whatever the lowering gives; say which in Body:.parse returns Result with refused!(..) text; in Nikaia it throws with the text kept byte for byte (the adapter maps it back to the same refused!). See docs/builder-facts.md for how a tools function’s error crosses.emit re-exports the moved types as it does pub use nikaia_std::tools::emit_kinds::EmitLifetimes as Lifetimes (:423), so callers keep emit::UserParallelism.crates/nikaia-std/src/tools/emit_build.nika: UserParallelism, ReentrancyCheck with parse, is_concurrent, is_on; parallelism takes has_threads: bool instead of a Target (the Rust caller passes target.has_threads()). Remove them from emit/mod.rs, re-export; Build’s hand impl Default. lower-std: only the new file, lowered.rs’s export line, and nothing else changes.RUST_TARGETS moves into emit_build.nika (the doc comment with the rustc --print target-list regeneration note goes with it); emit/rust_targets.rs is deleted. Report the lowered file’s size and lower-std’s work count (files re-lowered) under Tests:.it tests that name user-parallelism/reentrancy-check/an unknown target (find them with nikaia run scripts/where.nika -- NAME) pass unchanged, byte for byte in their messages; no new test needed unless a message moved (then a .stderr test in tests/compiler/tests/). Update docs/selfhosting-plan.md row E12-4 (4a done, 4b left) and run python3 scripts/self_hosting.py (report the %).it tests filtered on parallelism reentrancy target; nikaia --lib emit::; nikaia test tests/compiler --both-settings; the guard set of .claude/agents/builder.md; clippy clean. Commit lines emit: the build switches into Nikaia (E12-4a) and emit: the Rust target list into Nikaia (E12-4a), Part: #125. Changelog: none (a move).
The ~300-string list lowers to something rustc or clippy refuses and the fix is in the lowering (a compiler defect: fix it as its own commit with a test if small, else blocked with the probe); an open design choice; an error in another agent’s file.
Read docs/builder-facts.md.
crates/nikaia-std/src/tools/emit_core_calls.nika, its lowered/emit_core_calls.rs, crates/rs2nika/convert/**. Never stage them; if lower-std rewrites lowered/emit_core_calls.rs, leave it out of your commit and say so in Body:.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.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./home/user/Nikaia/docs/briefs/e12-4a.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 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); 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: say so 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