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agent: builder model: sonnet max_turns: 120 budget_usd: 20 —

Brief: E11-4b part 2, a_stmt of emit moves to Nikaia (Part of #583, after #854 part 1)

Score: S=2 (about 950 Rust lines), O=1 M (the last statement callback into Rust), C=12 M (E11-4a 1212 lines in one run; part 1 moved 290), self-hosting lane 1 (docs/priorities.md).

Facts

• Part 1 (d1fe8d04) moved blocks, stmt, stmt_written, makes_a_map into tools/emit_stmt.nika; a_stmt is still Rust, reached from Nikaia through the host method a_stmt (tools/emit_host.nika:81, emit/host.rs:294). Report: docs/briefs/b854-emit-stmt.report.md.
• a_stmt has about 25 callees: keep_plan, ty_counted, tethered_type, map_key, index_expr, around_value, handed_back, returns_either, … Those already in Nikaia are called directly; the rest stay host methods (add them to the host trait).
• rs2nika kept 0 of 116 lines in part 1 (stops at the first let-chain): write by hand from the Rust, use the draft only where it converts.
• If 950 lines do not fit the run: move a_stmt’s arms by statement kind (let/assign first, then return/loop/the rest), the unmoved kinds behind the host, and commit after each kind. Report what is left.

Locations (at bf655248; re-grep)

• crates/nikaia/src/emit/mod.rs: a_stmt 2398-3353, around_value 3354, handed_back 3366, returns_either 3393, map_key 3404, index_expr 3462, ty_counted 2096, keep_plan 4200, tethered_type 4226.
• Target: crates/nikaia-std/src/tools/emit_stmt.nika (prefix emit_stmt_). Pattern: tools/emit_expr.nika. Known facts: docs/builder-facts.md; names by nikaia run scripts/where.nika -- NAME.

To build

1. emit_stmt_a_stmt in tools/emit_stmt.nika with the helpers only it calls; emit_stmt calls it directly; the host’s a_stmt and Rust a_stmt go, with the helpers nothing else calls (dead locals deleted).
2. A lowering defect met: fix with a tests/compiler/ test, own commit, or file a ready issue and stop.
3. cargo build --profile fast -p nikaia, target/fast/nikaia lower-std: output unchanged beyond the slice’s files; cargo test --profile fast -p nikaia --test it -- emit:: sysroot, nikaia test tests/compiler --both-settings. Update scripts/self_hosting.py, add E11-4b switched to docs/selfhosting-plan.md. Last commit Fixes #854, #857, Part of #583.

Rules (CLAUDE.md)

• develop in the main checkout; git add <files> only; push fast-forward, no rebase. Commit after each step.
• Before pushing: cargo fmt, cargo clippy --all-targets -- -D warnings, scripts/pre-push-check.sh.
• No version lines, CHANGELOG.md, badges; no new NK code. New tests in Nikaia only; never the full suite.
• Do not touch other agents’ uncommitted files (git status at start); #856’s builder may work in tools/check_* and the emitter’s literal writers.
• NIKAIA_CACHE_LIMIT=2G; at most two clones with target/; delete target/release/nikaia-scratch; report GB freed. Scripts in files, small reads, no foreground sleep.

Report (at most 15 lines, <brief path>.report.md)

Result, Files, Commit, Fixes, Pushed, Tests, Deviation, Found, Needs, rs2nika kept N of M, Rust lines removed, GB freed, Owner (form: docs/architect.md, Briefs and reports).

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