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

v2: inferred views in fields, elements and struct literals (#1213 step 3)

Score: the language topics (owner, 2026-11-03), #1213 (ADR-views-3, option D). This step needs no new syntax: it is the checker half of views-3 D5. Read docs/specification/adr/adr-views-3.md D5 and D9, Part I 6.6, and #1152 (its probe) first. S=1, C~3-4 M.

Owns:

The checker and ledger parts in crates/nikaia-std/src/tools/ that decide whether a field or element holds a view (tether.nika, tiers.nika, text_tiers.nika, views.nika, view_changes.nika, ledger*.nika as the change needs), their lowered files, and new tests under tests/compiler/.

Not yours:

The parser (crates/nikaia/src/parser/mod.rs): keep is v3, from is v4; nothing here parses a new word.
keeps.nika, lowered/keeps.rs, contracts/keeps.rs, contracts/sync.rs (another lane): a change needed there stops the step and is reported under Needs:.
The specification text (v1).
tools/emit_*.nika, describe*.nika.

To build

A changed field or element holds an own value (D5): where a field or an element of a collection is changed in place, or handed to a parameter that keeps it, and a view (a piece of a buffer) would flow into it, the program is refused at the place the view flows in, with a help naming where to write .clone(). A field that only holds views stays a tethered view and is listed in the ledger’s tethered. Use the existing error code that refuses a view flowing where an own value is needed if one fits; if none fits, stop this piece and report it under Needs: (a new code is the supervisor’s). Tests: a struct whose field is built from a piece of a buffer and then changed (refused, help names .clone()); the same with .clone() (accepted); a map whose keys are pieces of a buffer and never changed (accepted, ledger lists the view). Commit Part of #1213.
A struct literal lends a local or a parameter as a call argument does (D5 last paragraph, #1152): building a struct, variant, tuple or list from a local or a parameter is no keep while the value stays in the function; the struct may not outlive what it lends. Read docs/briefs/bugs/b37-1152-ref-field-from-local.md.report.md first: it built part of this and left a question, which views-3 D5 answers: a struct holding a view of a local, handed back past that local, is refused (its probe under Found: (1) reaches rustc today; it must stop in the checker with the existing escape error). Tests: #1152’s probe (in #1213’s history, folded there) accepted; b37’s probe refused. Commit Part of #1213 (#1152 is closed into #1213).

A form Nikaia, std or the toolchain lacks is sorted per CLAUDE.md A missing form stops the work. A further defect: no second fix in this brief, file nothing, report it under Found: with its probe.

Rs2nika: none.

Done when

Both rules hold with tests (or a blocker is reported with its probe). nikaia test tests/compiler --both-settings and tests/errors give every count as before plus the new tests; the it tests filtered on view, tether, ledger; the guard set of .claude/agents/builder.md. Clippy clean; the lower-std fixpoint holds; the committed ledgers of crates/nikaia-std and the packages unchanged or their change explained in Body:. No changelog line.

Stop and report if

a .stderr of an existing test changes in a way the rule does not explain; the work needs keep or from parsed (that is v3 and v4: stop, report under Needs:); the work needs a change in keeps.nika.

Rules (CLAUDE.md; shared checkout)

Read docs/builder-facts.md first. You work in /home/user/Nikaia on develop (the shared checkout). Build with CARGO_INCREMENTAL=0 cargo build --profile fast -p nikaia; use only /home/user/Nikaia/target/fast/nikaia.
git add <files> only, never -a/-A; commit after each step. Never git reset, stash, checkout ., restore .; restore only your own files by name. An error in another agent’s file is escalated, not touched.
Commit every lowered file lower-std changed, yours and others’. Do not edit docs/selfhosting-plan.md, docs/architect.md, docs/priorities.md, docs/bootstrap.md or scripts/self_hosting.py: rows for them go into Body: of your report.
Before committing: cargo fmt, cargo clippy --all-targets -- -D warnings, nikaia run scripts/pre-push.nika, and the gate of .claude/agents/builder.md. You commit; the supervisor pushes.
No version lines, CHANGELOG.md, badges; no new NK code. New tests in Nikaia only; never the full suite. No foreground sleep, no polling; scripts in files.
Disk is small: NIKAIA_CACHE_LIMIT=2G; if df -h /home/user shows under 2 GB free, stop and report blocked. Never delete another checkout’s target/.

Report (at most 15 lines, to exactly `/home/user/Nikaia/docs/briefs/views/v2-inferred-views.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 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 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:); 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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