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agent: builder model: opus max_turns: 120 budget_usd: 25 —

Brief: P5d, check, newly, keeps_that_moved and explain of project.rs into project_check.nika (Part #125)

Score: self-hosting lane, bootstrap lane 1 (docs/bootstrap.md). Plan row P5d of docs/selfhosting-plan.md, Large files 3 (draft 54 %; prerequisite P2 built). S=2, C~3-5 M (comparable: M3b, P4b). First of the batch; P5b (lower_reading, same file, other lines) runs after it.

Cut: crates/nikaia/src/project.rs:1193-1488 Cut: crates/nikaia/src/project.rs:1490-1674 Convert: –profile check-free –prefix project_check_ Shape: schematic host-calls (R47/R244 [forms project_check_] rows and R295’s host parameter, learned: P4b)

The driver converts this before you start (.draft.nika, .notes, .rs). Ranges at 02b36d6; if git log -- crates/nikaia/src/project.rs shows a later change, re-grep pub struct Around<, ^fn newly, pub fn changed_lines, pub struct Explain, ^pub fn explain( and cut again. Project::report (2473-2578) is not in this row: it reads and emits a whole Program, which P5b’s host gives; it moves with P5c.

If crates/nikaia-compiler/src exists, R0 (#921) has run: read crates/nikaia-std/src/tools as crates/nikaia-compiler/src, nikaia_std::tools:: as nikaia_compiler::.

Facts

• Read docs/builder-facts.md (new: Host traits, the anchored it filter, let mut x: String = "…", #943).
• Already Nikaia (do not redo): project_check_summary, the three project_check_let_*/lint_* filters, the locked_* messages (project_check.nika); Ledger, Contract (fails_with, keeps, signature: Signature?), Signature.params, Ty.text() (ty.nika); CheckFinding/CheckSeverity (check::Finding re-exports them, check/mod.rs:46); [forms] already maps {x}.span.at() to ({x}.span.start as i64).
• Stays Rust: Around, check::Newly/Kept (read in check/*, lane 2), Explain and asked() (built by main.rs:457, :771 from flags; Nikaia’s field would be comptime_), write_proofs (Book is Rust), write_ledger and changed_lines (already thin over P2’s messages and diffs.nika; the with_context chain must stay byte for byte), foreign_library. Every Rust function keeps its signature (callers: lower_reading project.rs:953, sysroot.rs:308/582, specbook.rs:208, main.rs:473, and it tests common/mod.rs, sequences, compile_time_reads, grammar_at_build_time, prove, build_time).
• Step 1, the draft’s host calls: add a [forms project_check_] and [hosts project_check_] section to crates/rs2nika/convert/rs2nika.names (format: the project_members_ sections there) for the Rust calls below, re-convert, and build from that draft; --score against it. Re-convert with the driver’s two commands (C=crates/rs2nika/convert/target/nikaia/bin/rs2nika; $C --cut crates/nikaia/src/project.rs:1193-1488 --cut crates/nikaia/src/project.rs:1490-1674 > D.rs; $C --profile check-free --prefix project_check_ --file D.rs > D.nika 2> D.notes). The table is data, not converter code: the converter lane’s uncommitted crates/rs2nika/convert/nikaia.* are not yours.
• pub trait ProjectCheckHost (Rust impl CheckHost in project.rs, built by check over parsed, around, own, library = foreign_library(foreign)?, modules = foreign.packages(modules); RefCell for the facts and the violations):
  • fn check_against(ref self) -> Vec[CheckFinding] sync (check::check_against(..); keeps checked.facts for facts_out)
  • fn foreign_check(ref self) -> Vec[CheckFinding] sync (crate::foreign::check(..))
  • fn sync_violations(ref self) -> i64 sync (sync::check(..), kept)
  • fn render_sync_violation(ref self, at: i64, path: ref String, source: ref String) -> String sync
  • fn render_finding_in(ref self, finding: ref CheckFinding, path: ref String, lines: ref Vec[String]) -> String sync
  • fn in_the_wrapper(ref self) -> bool sync (WRAPPER_MARKER set or WARNED)
  • fn eprint(ref self, text: ref String) sync (std has no eprint without a newline)
• Nikaia project_check_check[H: ProjectCheckHost](host: ref H, path: ref String, source: ref String, user_parallelism: ref String, refuted_claims: ref String, unproved_claims: ref String, building_a_library: bool) -> ProjectCheckSaid with pub struct ProjectCheckSaid { warnings: String, refused: String? }: the NK1238 retain, the sort, the three filters, the printing loop, the summary. Rust: refused -> Err(diagnostics::refuse(text)), else Ok(warnings); facts_out filled from the host.
• Nikaia project_check_gained(committed: ref Ledger, inferred: ref Ledger) -> collections::BTreeMap[String, Vec[String]] and project_check_keeps_that_moved(committed: ref Ledger, inferred: ref Ledger) -> collections::BTreeMap[String, Vec[ProjectCheckKept]] (ProjectCheckKept { param: String, now: bool, ty: String }; signature.arguments() is signature.params, check contracts/mod.rs:123). Rust newly keeps reading and parsing nikaia.contracts and maps ProjectCheckKept to check::Kept.
• pub trait ProjectCheckExplainHost (Rust impl over &Program, &Settings, &Reads, std_ledger()): fn units(ref self) -> i64 sync, fn unit_path(ref self, at: i64) -> String sync, fn unrolling_report(ref self) -> String sync, fn explain_report(ref self, kind: ref String, at: i64) -> String sync (kinds overlaps, sharing, tethers, asserts, bounds, trust: one arm each, the NO_COLOR/terminal test inside asserts). Nikaia project_check_explain[H: ProjectCheckExplainHost](host: ref H, comptime_asked: bool, kinds: ref Vec[String]) prints in today’s order; Rust explain keeps asked() and passes the asked kinds in that order.
• Every refusal, warning and report byte for byte (tests/compiler .stderr, the --explain tests).
• Do not touch: crates/rs2nika/** except rs2nika.names, contracts/*, check/*, emit/* (lane 2), manifest.*, modules.*, docs/briefs/* other than your report, and the uncommitted files git status shows at start.
• Disk: about 3.7 GB free at 02b36d6; agent.nika escalates under 3 GB. Copy target/fast/nikaia to your scratch dir before a long test run; right before it, git status --short the lowered files.
• Tests: --lib project::; it filters project check newly keeps explain asserts sharing overlap tether bounds trust compile_time_reads prove build_time sequences; nikaia test --project tests/compiler; lower-std fixpoint (only lowered/project_check.rs and the index change).

To build

1. The rs2nika.names rows, the two hosts, project_check_check, project_check_gained, project_check_keeps_that_moved, project_check_explain into project_check.nika with doc comments; check, newly, keeps_that_moved, explain forward. Commit project: the check's tally and the explanations into Nikaia (P5d), Part: #125; plan row P5d updated (built, what stays Rust, report moved to P5c), self-hosting share in the commit body.

Rules (CLAUDE.md; this block is pasted into every brief, also a fix-forward)

• Read 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).
• Before pushing: cargo fmt, cargo clippy --all-targets -- -D warnings, scripts/pre-push-check.sh, and the gate of .claude/agents/builder.md (#852).
• No version lines, CHANGELOG.md, badges; no new NK code. New tests in Nikaia only; never the full suite. No foreground sleep, no polling; scripts in files.
• Disk: 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.

Report (at most 15 lines, to exactly /home/user/Nikaia/docs/briefs/p5d-project-check.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 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:); 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

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