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Brief: #1107, a ref T? map view unwrapped by ?? return null or a match binding loses ref

Blocks: c1c-ledger-lookup.md (C1c: LedgerOps::lookup moves to (String, ref FnContract)?; C1b, the stored fold, runs meanwhile)

Score: compiler bug, a wrong refusal of what Part I allows (an element read is a view, ADR-282 D7, ADR-293 D28), blocks a self-hosting move. Cause suspected, not traced to the line: medium.

Facts: Where things live, Traps already met, Commands

Issue #1107

A ref T? view (a map index into a ref parameter) unwrapped by ?? return null or by a match binding loses its ref: the value is typed as owned T, so it cannot be bound to a ref T local nor handed back as the ref T part of a tuple. Part I (the views section, let first: ref Expr = given[0]) and ADR-282 D7 make an element read a view; the unwrapped value is the same element. Found tracing C1b (LedgerOps::lookup, contracts/mod.rs:548: self.functions.get(name).map(|c| (name.to_string(), c))), which it blocks.

Probe (checked by the architect on target/fast/nikaia at 7ad2ea08)

use std::collections
struct C { n: i64 }
fn lookup(m: ref collections::BTreeMap[String, C], k: String) -> (String, ref C)? {
    return match m[k] {
        null => null,
        c => (k.clone(), c),
    }
}
fn main() {
    let mut m = collections::BTreeMap()
    m.insert(f"a{1}", C { n: 5 })
    let hit = lookup(m, f"a{1}")
    println(f"{hit?.0 ?? "-"} {(hit?.1)?.n ?? 0} {lookup(m, f"b{1}")?.0 ?? "-"}")
}

Expected a1 5 -. Got NK1104 You're returning `(String, C)?`, but the function is declared to return `(String, ref C)?`.

Rows (same C, m: ref collections::BTreeMap[String, C], k: String, xs: ref Vec[C]):

body result
the probe’s match into (String, ref C)? NK1104 (String, C)?
let c: ref C = m[k] ?? return null NK1103 “This value is C, but the let declares ref C”
let c: ref C = m.get(k) ?? return null NK1103, the same
let c = m[k] ?? return null / return (1, c) into (i64, ref C)? NK1104 (?, C)
let c = m[k] ?? return null / return c into ref C? NK1104 C
return m.get(k) into ref C? NK1104 C? (m[k] passes)
return m[k] into ref C? passes (must stay)
let c: ref C = xs[0] / return (1, c) into (i64, ref C)? passes (must stay)

To build

  1. Reproduce every row (Tests:).
  2. Trace where the unwrapped value’s type drops the view (the ?? with a jump, the match arm binding over a T? scrutinee, and BTreeMap.get over a ref map against m[k]), and keep it a view of the same read. Lowering: Option<&C> / (String, &C); any lowering rustc accepts.
  3. lower-std and its fixpoint.
  4. Test tests/compiler/tests/an_unwrapped_map_view_stays_a_view.nika + .stdout: the probe and rows 2-6 as functions. Fails on the unfixed binary.

Commit check: a view unwrapped by ?? or a match stays a view (Fixes #1107).

Suspected location (medium confidence)

Done when

The new test fails on the unfixed compiler and passes through nikaia test --project tests/compiler --both-settings; the tests named coalesce|view|map_read|element_read pass; lower-std fixpoint clean; build, fmt, clippy, pre-push-check.sh; committed locally. Changelog: one line. Stop about 15 turns before max_turns: commit what is finished and report partial.

Stop and report if

An edit is needed outside crates/nikaia-std/src/tools/check_*.nika, their lowered twins, lowered.rs, the emitter files for the lowering (emit_*.nika) and the new test. Or you hit an error in another agent’s file.

Not yours, never stage: every file git status shows modified or untracked at your start, and every docs/briefs/* file except your report.

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/bugs/b26-1107-unwrapped-map-view.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 or red <check>: your cheap checks, never none, which cuts the batch, j4 2026-10-31), 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 a lowering other than the brief’s where rustc cannot take the brief’s, b1029 2026-10-31: say why 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:, nor an existing test’s expected .stdout/.stderr updated because your change rightly changes the message it prints, b1012b 2026-10-31: name the test 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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