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agent: builder model: opus max_turns: 120 budget_usd: 30 —

Brief: #869 steps 1, 2, 4: a null test narrows a path of fields (ADR-382 D2, D3, D5)

Score: S 2 (builds a decided, specified rule, 0.0.1227; today if p.name != null { p.name.len() } is a false NK1125), O 1 M (the converter’s if let Some(x) = &self.f gap, step 6 later), C 8 M (#655 check+lowering runs), bugs lane (no open compiler bug is ready besides #871).

Issue text (#869)

ADR-382 (docs/specification/adr/adr-382.md, read D1-D5 first; Part I 10-nikaia-light.md ~:592) decided that a null test narrows a path of fields from a local or a parameter, not only a name. Probe (must run after this brief):

struct P { name: String?, age: i64 }
fn main() {
  let mut p = P { name: "a", age: 1 }
  if p.name != null { p.age = 2; print(p.name.len()) }   // sibling write keeps it
}

Locations

To build (each its own commit, Part of #869)

  1. Check: key the proofs by a path (root plus field list), not a name alone; a path is proved in every place D2 lists.
  2. D5: the proof ends at an assignment to the path or a prefix, at a mut hand-over (a ref mut self method, a mut argument), and at a lambda, task, overlap branch or select arm that sees the root. A loop doing one of these ends it for the whole loop. NK1102 names the write.
  3. (issue step 4) Lowering: a use of a proved path is written .as_ref().unwrap(), or .as_mut().unwrap() where written through.
  4. Tests in tests/compiler/tests/ (.nika + .stdout/.stderr), one each: a path narrowed in each D2 place; a sibling write that keeps the proof (the probe); a ref mut self call that ends it; an assignment to a prefix that ends it. Not in this brief (next brief, b869b): issue steps 3 (v[i].f not a path), 5 (if let refused), 6 (converter, gaps row, ADR Built cell).

Done when

Steps 1-4 built, the probe runs; lower-std clean; nikaia test tests/compiler --both-settings; it filters nullable, narrow, views_kept, match_arms and the guard set of .claude/agents/builder.md. Changelog: one line (a path of fields narrows after a null test, ADR-382).

Stop and report if

D2/D5 leave a case open that the tests need (Owner: only if the ADR truly does not answer it), or an error in another agent’s file.

Read docs/builder-facts.md.

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

Report (at most 15 lines, to exactly /home/user/Nikaia/docs/briefs/b869a-path-narrowing.md.report.md)

Fields of docs/architect.md, Briefs and reports: Result: done|noop|partial|blocked (the bare word first; Owner: is a question for the owner or none, never a role), Files, Commit, Fixes, Pushed, Tests, Gate (green|red), Deviation, Found, Needs, Changelog, Owner, Disk freed. 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); 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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