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agent: builder model: opus max_turns: 90 budget_usd: 18 effort: medium —

Brief: #1161 collect items of T? into a declared Vec[T]?

Blocks: the grammar_run move step 2 (type_written, #125)

Score: found during the self-hosting moves (#125), 2026-11-02; the issue holds the decision and the probe.

Facts: Where things live, Traps already met, Commands

Problem

Approved extension of ADR-293 (read #1161): collect into a declared C[T]? from items of T? yields null at the first null item. Today NK1103. Probe: /tmp/claude-0/-home-user-Nikaia/b7e2d91b-1a15-5371-a36e-8c201aeab2d2/scratchpad/m2/p3/main.nika.

To build

1. The ADR-293 sentence and its place in docs/specification/30-nikaia-tooling.md, the checker accepting it, the lowering to collect::<Option<_>>(). Test tests/compiler/collect_into_optional_list.nika + .stdout. Commit Fixes #1161. Run the tests your change touches (nikaia test on the new test, the --test it filters of the files you change); lower-std and its fixpoint if a tools/*.nika changed.

Rules

• Read .claude/agents/builder.md and docs/builder-facts.md first. Commit locally with target/fast/nikaia run scripts/commit.nika -- REPORT (if it refuses because another agent’s files are staged, git commit --only <your files>); the driver pushes.
• Version lines, CHANGELOG.md, badges and NK codes are the supervisor’s.
• No cause after about 60 turns: stop, Result: partial with what you ruled out and the suspected file and function.

Report (at most 15 lines, to exactly /home/user/Nikaia/docs/briefs/bugs/b40-1161-collect-into-optional.md.report.md)

Fields of docs/supervisor.md, Briefs and reports. Final answer, one line: done <sha>, report <path> (or BLOCKED: ...).

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