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

Brief: std::regex, the first package - run-time patterns, no positions (#673 step 1)

Owner’s direction (2026-10-28): start with everything on regex::Dynamic (the floor of ADR-regex-1 D6), add the rest step by step; leave positions out until ADR-374 is built. Records: docs/specification/adr/adr-regex-1.md (D1-D3, D8, D10), Part I 2.6 (the std::regex paragraph).

Facts

To build

  1. The type and the engine. regex::Regex[E] with E: regex::Engine (a trait), and exactly one engine, regex::Dynamic. regex::dynamic(pattern: String) -> regex::Regex[regex::Dynamic] throws regex::Error; regex::Error carries the crate’s message as text (no crate type). The type parameter is there from the start so that a program’s type does not change when engines are added (ADR-regex-1 D3).
  2. The calls without positions (ADR-regex-1 D3’s table, minus start/end/from:), each on regex::Regex[regex::Dynamic]:
    • re.is_match(s: String) -> bool
    • re.find(s) -> text::Match? (the leftmost-first match; m.text() is its text, a view of s)
    • re.find_all(s) -> Seq[text::Match] (left to right, not overlapping)
    • re.captures(s) -> regex::Captures?, c.group(i: i64) -> text::Match? (0 is the whole match; a group that did not take part is null; an i past the groups is null), c.named(name: String) -> text::Match?
    • re.replace_all(s, with: String) -> String ($1, ${name} as the crate’s interpolation does)
    • re.split(s) -> Seq[ref String] (the pieces between matches, views of s) Regex is read-only and shared between threads: say so in the ledger as the other shared std types do.
  3. Tests in Nikaia in tests/compiler/tests/ (.nika with .stdout, a refusal with .stderr): one test per call above; a multibyte text ("äöü 12 €") for find and split; find_all not overlapping ("aaaa" with aa); a group that did not take part; named; replace_all with $1 and ${name}; a bad pattern ("(") caught as regex::Error and its message printed; a literal pattern passed to dynamic (allowed).
  4. Add "regex" to the module list of every_std_module_is_in_the_shipped_ledger (crates/nikaia/tests/it/contracts.rs :814) - an existing Rust test changed to keep it true, no new one.

A compiler defect met (a generic std type with a bound the ledger cannot describe, a view result it cannot type, a Seq of a std struct) stops the slice: fix it in the compiler as its own commit with a test if it is one step, else report it under Needs: with a probe of a few lines. Do not route around it - no i64 positions, no String copies instead of views, no type without its parameter.

Done when

The new tests pass with target/fast/nikaia test --both-settings --project tests/compiler; the guard set of .claude/agents/builder.md; clippy clean; lower-std unchanged or at its fixpoint. Commit std::regex: run-time patterns on regex-automata, without positions (#673 step 1), Part of #673. Changelog: one line for the supervisor’s heading under Changelog: (what a program can now write).

Stop and report if

An open design choice beyond this brief (the shape of a call, a name); a .stderr outside your tests that would change; 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/b673-regex-dynamic.md.report.md)

Fields of docs/architect.md, Briefs and reports: Result: done|noop|partial|blocked (the bare word alone), Files, Commit, Body (optional), Fixes, Pushed, Tests, Gate (green|red), Deviation, Found, Needs, Changelog, Owner, Disk freed, Rs2nika: none. none where nothing, as the bare word. Final answer, one line: done <sha>, report <path> (or BLOCKED: ... / PUSH REJECTED ...).

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