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

Brief: P5b, lower_reading of project.rs into a new project_lower.nika (Part #125)

Score: self-hosting lane, bootstrap lane 1 (docs/bootstrap.md). Plan row P5b of docs/selfhosting-plan.md, Large files 3 (draft 36 %; prerequisites M3b built in 093923c, P5d before it in this batch). S=2, C~4-6 M (comparable: M3b). Narrowed from the plan row: lower, reads_for, reads_for_file, read_file, packages_of_file are adapters already, project_for_file’s name rule needs is_ascii_alphanumeric (#924) and foreign_library needs std_library (Rust): all stay.

Cut: crates/nikaia/src/project.rs:730-1108 Convert: –profile check-free –prefix project_lower_ Shape: schematic host-calls (R47/R244 [forms project_lower_] rows and R295’s host parameter, learned: P4b, P5d)

The driver converts this before you start. Ranges at 02b36d6; P5d (same file, lines below) runs first, so re-grep ^pub fn lower_reading( and the Ok(Lowered { that ends it, and cut again if they moved.

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 (Host traits: a throws host method, an anyhow error kept in a RefCell and handed back unchanged, as M3b’s ModulesEmitHost, modules.nika).
• Already Nikaia (do not redo): Ledger, Contract (requires, ensures, from, inferred), Published (prover_results.nika:85, Rust crate::prove::Published), changed_contracts (contract_changes.nika:17, takes mine and implies callbacks; Rust prove::changed_contracts wraps it), modules_program_of/modules_emit_reading (M3b), project_check_check (P5d).
• Stays Rust: the Lowered struct and lower_reading’s signature (callers: lower, project_for_file, main.rs, sysroot.rs, it tests: nikaia run scripts/where.nika -- lower_reading lower); the choices assembly before the program is read (Layout, reads_for, build_for_cpu, Choices, the proofs digest: 737-765); Program (held by the host); Cache, Artifacts, Book, with_book, cexport; the export assembly after the call (1070-1094, the digest replaced in header, python, node).
• Step 1, the draft’s host calls: add [forms project_lower_] and [hosts project_lower_] sections to crates/rs2nika/convert/rs2nika.names for the calls below, re-convert (C=crates/rs2nika/convert/target/nikaia/bin/rs2nika; $C --cut crates/nikaia/src/project.rs:A-B > D.rs; $C --profile check-free --prefix project_lower_ --file D.rs > D.nika 2> D.notes), build from that draft, --score against it.
• pub trait ProjectLowerHost (Rust impl LowerHost in project.rs, built after the choices with layout, settings, reads, packages, input, no_cache; RefCell for program, cache, choices, exported, foreign, checked_facts, proofs, published, and a kept anyhow::Error):
  • fn read_program(ref self) throws (defaults_compiled_in + the three read_*, entry_shown_as; then choices.naming(shown_paths))
  • fn open_cache(ref self) sync (the Cache::open and its warning, unless no_cache)
  • fn key_source(ref self) -> String sync, fn source_paths(ref self) -> Vec[String] sync, fn could_promise(ref self) -> String sync, fn dependencies(ref self) -> collections::BTreeSet[String] sync
  • fn committed_ledger(ref self) -> Ledger? sync (in a project, nikaia.contracts read and parsed; null otherwise or on any failure)
  • fn lost_sync(ref self, committed: ref Ledger) -> String sync
  • fn export(ref self) throws (the settings.library() branch, kept for after the call)
  • fn cached(ref self) -> ProjectLowerArtifacts? sync (lookup + has_all), fn record(ref self, made: ref ProjectLowerArtifacts) sync (record + save, its warning)
  • fn in_the_wrapper(ref self) -> bool sync, fn eprint(ref self, text: ref String) sync
  • fn check_units(ref self) -> String throws (886-974: foreign, newly, Around, promised, the book, the per-unit check; returns the warnings, keeps book and facts)
  • fn emit(ref self) -> String throws (975-990: the second with_book, described, checked_facts, emit_reading; keeps published and the program, proofs in a project; returns the Rust)
  • fn contracts(ref self) -> Ledger sync, fn published(ref self) -> collections::BTreeMap[String, Published] sync, fn render(ref self, ledger: ref Ledger) -> (String, String) sync (render, render_derived)
  • fn unused_reads(ref self) -> Vec[String] sync
  • fn changed_contracts(ref self, now: ref Ledger, committed: ref Ledger) -> String sync (with the dependencies filter), fn parse_ledger(ref self, text: ref String) -> Ledger? sync
• Nikaia project_lower_reading[H: ProjectLowerHost](host: ref H, in_project: bool) -> ProjectLowerOut throws with pub struct ProjectLowerArtifacts { rust: String, ledger: String, derived: String, warnings: String } and pub struct ProjectLowerOut { rust: String, ledger: String, derived: String, sources: Vec[String], reused: bool, notes: String }: the order of the steps, the cache hit’s replay, the published-contract merge (994-1015, over Ledger in Nikaia), the allowlist warning, the notes. Rust builds Lowered from it plus proofs and the export.
• Every warning, note and refusal byte for byte and in the same order on stderr (tests/compiler .stderr).
• Do not touch: crates/rs2nika/** except rs2nika.names, contracts/*, check/*, emit/* (lane 2), modules.*, manifest.*, project_check.* (P5d’s), docs/briefs/* other than your report, and the uncommitted files git status shows at start.
• A new tools/*.nika file: one lower-std run with the old binary before cargo build, and a row in scripts/self_hosting.py (builder-facts.md, A new .nika).
• 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 cache lower ledger prove proofs export library described foreign allowlist reads warnings + guard set; nikaia test --project tests/compiler; lower-std fixpoint (only lowered/project_lower.rs and the index change).

To build

1. The rs2nika.names rows, the host, the two structs and project_lower_reading into a new project_lower.nika with doc comments; lower_reading forwards. Commit project: a lowering's steps, its cache and its ledger into Nikaia (P5b), Part: #125; plan row P5b updated (built, narrowed, what stays Rust), 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/p5b-project-lower.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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