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agent: builder model: opus max_turns: 70 budget_usd: 16 —

Brief: #1033, a guard cannot read a text(..) label whose pattern binds names

Score: a compiler defect found by y2c (#928 step 2b, blocked); the package waits on it, second after #1032 (y11).

Facts earlier grammar builders paid for: a rustc error from a grammar (Mismatched types, Cannot find value) is the emitter’s or the checker’s: run nikaia check (passes here) and nikaia lower FILE (writes the .rs, shows the rule’s lowered type) first. The backend is winnow-grammar (pinned rev, cargo checkout, not changed here). nikaia test --both-settings --project tests/compiler runs over 10 minutes: run_in_background with timeout: 3600000. If other sessions’ uncommitted files block git pull --rebase, push fast-forward and report Pushed: rejected (the driver rebases).

Issue (#1033, copied)

Found by the yaml lane (y2c, #928 step 2b, 2026-10-31): the y2 draft’s Double rule, s:text(parts:DoublePart*) ... if(fits(k, s), ..). A compiler defect, fixed in the compiler (CLAUDE.md).

Probe (the architect ran it on 506edc2d)

grammar G {
	rule WS = "" -> { }
	rule Ch -> i64 = x:any if(x >= '0' && x <= '9') -> { 1 }
	entry rule top -> String = s:text(d:Ch+) if(s.len() > 1, "two digits") eof -> { s }
}
fn main() {
	let r = G::top("12") catch {
		println("error")
		return
	}
	println(r)
	let e = G::top("1") catch {
		println("error")
		return
	}
	println(e)
}

nikaia check passes; nikaia run fails in rustc: Cannot find value s (4:43). Without the inner label, s:text(Ch+), it prints 12, error.

Cause (architect, from nikaia lower)

A text(..) whose pattern binds names (#1013) is lowered as (d:Ch+) @ __nikaia_s_from, and s itself is bound only in the action’s prelude (emit_grammar.nika:393-401, let s = ::nikaia_std::grammar::covered(input, __nikaia_s_from.start..__nikaia_s_from.end);). The guard is emitted inside the pattern (emit_pattern.nika:153, Pattern::Guard), before the action, where only __nikaia_s_from/_to exist. Lowered line: (d:Ch+) @ __nikaia_s_from if(s.len() > 1, "two digits") eof.

Locations

To build (one commit)

  1. A guard that names a binding text(..) label bound before it sees that label as text: e.g. the guard’s expression wrapped in a block that first binds each such label it names, as the prelude does (covered / covered_bytes), only for labels whose edges are already bound at the guard. Any lowering rustc accepts. Test tests/compiler/tests/grammar_a_guard_reads_a_binding_text_label.nika with .stdout 12, error (the probe), failing on the unfixed binary. Fixes this issue.

Done when

The new test passes and failed before, the grammar_ tests pass, the gate of .claude/agents/builder.md (#852) is green.

The commit says Fixes #1033. Changelog: one sentence (this changes crates/).

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/yaml/y12-1033-guard-text-label.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 a test’s expected .stdout/.stderr taken from what the program really prints where the brief’s sketch of it was short or wrong, b934 2026-10-29: say so in Body:, nor a lowering that follows the ADR governing it where the brief’s expected lowering contradicts that ADR, b933 2026-10-29: name the ADR 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_01UVxJDveRM5qKZKyCqq6Y24

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