agent: builder model: sonnet max_turns: 60 budget_usd: 10 —

Brief: #1106, text holding both kinds (`EitherText`) bound to `fs::Path` passes check and fails in rustc

Blocks: k3b-comptime-bundle.md (K3b run 2, docs/briefs/k3b-comptime-bundle.md.report.md; its move waits on branch wip/k3b-comptime-bundle-run2 707d5e53)

Score: compiler/std defect that blocks a self-hosting move (K3b); small, cause known.

Facts: Where things live, Traps already met, Commands

Issue #1106 (probe checked by the architect on `target/fast/nikaia` at 7ad2ea08)

struct Holder { name: String }

fn to_path(h: ref Holder, c: bool) -> fs::Path {
    let mut x = "none"
    x = if c { h.name } else { f"a{c}" }
    let p: fs::Path = x
    return p
}

fn main() {
    let h = Holder { name: f"abc{1}" }
    let a = to_path(h, true)
    let b = to_path(h, false)
    println(f"{a.file_name() ?? "-"} {b.file_name() ?? "-"}")
}

Expected abc1 afalse. Got rustc: The trait bound `PathBuf: From<EitherText<'_>>` is not satisfied (x holds both kinds, ADR-282 D13, D14; let p: fs::Path = x lowers to PathBuf::from(x)).

Location (high confidence)

crates/nikaia-std/src/either_text.rs: the From impls (lines 63-92 and 287, impl From<EitherText<'_>> for String). K3b verified that impl From<EitherText<'_>> for std::path::PathBuf fixes its case; move owned text in without a copy where the value holds one (follow the String impl at 287).

To build

Reproduce the probe on the unfixed binary (Tests:).
The From impl in either_text.rs.
Test tests/compiler/tests/either_text_into_path.nika + .stdout: the probe as written. It fails on the unfixed binary. Also run the tests named either|mixed_arms|path. Commit std: text holding both kinds converts into fs::Path (Fixes #1106).

Done when

The new test fails on the unfixed compiler and passes through nikaia test --project tests/compiler --both-settings; build, fmt, clippy, pre-push-check.sh; committed locally. Changelog: one line.

Stop and report if

An edit is needed outside either_text.rs 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 (now: tools/emit_core_leaves.nika and its lowered twin, b22’s), and every docs/briefs/* file except your report.

Rules (CLAUDE.md; this block is pasted into every brief, also a fix-forward)

Read docs/builder-facts.md first. develop in the main checkout; git status at start: other agents’ uncommitted files are not yours, never touch or stage them.
git add <files> only (scripts/commit.nika -- REPORT does it); commit locally after each step and never push: the driver runs the complete suite and pushes (.claude/agents/builder.md, Cheap checks only; owner, 2026-10-31).
Before committing, cheap checks only: cargo build --profile fast -p nikaia, lower-std and its fixpoint when a tools/*.nika changed, cargo fmt, cargo clippy --all-targets -- -D warnings, scripts/pre-push-check.sh, the tests the brief names and the ones your change touches. No gate.nika.
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.
A form Nikaia, std or the toolchain lacks stops the work: no code around it unless an ADR or Part I-III refuses it (name it). Else Result: blocked, Found: gap + probe, Needs: architect decision (CLAUDE.md, A missing form stops the work).
Disk: NIKAIA_CACHE_LIMIT=2G; at most two clones with target/ in the machine; delete your own clone’s target/ and target/release/nikaia-scratch at the end; report GB freed.
Time box: no cause after about 40 turns, or going in circles: stop, Result: partial with what you ruled out, the probe, and the suspected file and function (.claude/agents/builder.md).
Write the report, then commit with target/fast/nikaia run scripts/commit.nika -- REPORT, which writes Pushed: local <sha> into it. A report without a Pushed: line, or with a placeholder left in (TC, DISK), is not done and cuts the batch (k3a1 2026-10-29: Result: done, nothing committed).

Report (at most 15 lines, to exactly `/home/user/Nikaia/docs/briefs/bugs/b25-1106-either-text-into-path.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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Brief: #1106, text holding both kinds (EitherText) bound to fs::Path passes check and fails in rustc

Issue #1106 (probe checked by the architect on target/fast/nikaia at 7ad2ea08)