Point setup-rust-toolchain at the crate, and record the corrections

A review finding on this PR, verified against the action's own
documentation: `defaults.run.working-directory` governs `run:` steps
only. Each `actions-rust-lang/setup-rust-toolchain` step executes from
GITHUB_WORKSPACE, where this repository is a subdirectory and no
toolchain file is visible, so it would silently install `stable`
instead of the pin. `rust-src-dir` is the input that points it at the
crate — the same directory that now holds the single
`rust-toolchain.toml`, beside `.cargo/config.toml`.

The reviewer's suggested value was the repository root, which was
correct against the commit it read. It is the crate directory here,
because the root toolchain file was removed in the previous commit
rather than kept in sync.

The board's PR entry gains an appended correction rather than an edit,
per its own append-only rule, covering the four claims that first entry
got wrong: the repo did have a toolchain pin, the push trigger is
limited to `main`, `--manifest-path` is not equivalent to running in the
crate directory, and `-D warnings` is no longer unmeasured.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AGVLyRZNEKKBSfBDJfbY3V

Author: claude

.claude/board/PR_ARC_INVENTORY.md

@@ -34,6 +34,32 @@ first real measurement, with the tiered `continue-on-error` +
 `TECH_DEBT.md` fallback named in the PR body if it comes back red on
 pre-existing debt.
 
+**Correction (2026-09-05, head `1ea5c85`).** Appended per the append-only
+rule rather than edited above; the original lines stay as written.
+
+- *"this repo had neither a workflow directory nor a toolchain pin before
+  this PR"* — the workflow half is right, the toolchain half is not.
+  `native/lgj-abi/rust-toolchain.toml` already pinned `1.97.1`. Adding a
+  second file at the repository root made two pins for one toolchain, and
+  cargo reads whichever is nearest the working directory. The root file is
+  removed; the crate-level file is the authority, now `1.98.1` — forced,
+  since `ndarray` 0.17.2 declares `rust-version = "1.98"`.
+- *"runs on every push/PR"* — the `push` trigger is limited to `main`, so
+  the accurate statement is every pull request and every push to `main`.
+- *"all scoped to `native/lgj-abi` via `--manifest-path`"* — that scoping
+  is what broke the first run. Cargo reads `.cargo/config.toml` from the
+  working directory's ancestry, never from the manifest's directory, so
+  the crate's `-Ctarget-cpu` baseline was dropped and
+  `the_x86_64_build_has_a_vector_baseline` failed exactly as designed. The
+  jobs now set `working-directory` to the crate, and CI exports the v3
+  baseline explicitly because GitHub-hosted runners do not guarantee
+  AVX-512. Each `setup-rust-toolchain` step also gained `rust-src-dir`:
+  `defaults.run.working-directory` governs `run:` steps only, so without it
+  the action reads no toolchain file and falls back to `stable`.
+- *"whether `-D warnings` is clean on `lgj-abi` today is unmeasured"* — now
+  measured locally: clippy and fmt clean, 138 unit tests plus the G11 fence
+  passing, under the same commands CI runs.
+
 **Docs.** `LATEST_STATE.md` entry; this entry.
 
 **Confidence.** High that the workflow shape is correct (it is a direct

.github/workflows/lint.yml

@@ -47,6 +47,13 @@ jobs:
           path: lance-graph-java
       - uses: actions-rust-lang/setup-rust-toolchain@v1
         with:
+          # `defaults.run.working-directory` applies to `run:` steps only, NOT
+          # to action steps: this action executes from GITHUB_WORKSPACE, where
+          # the checkout is a subdirectory and no toolchain file is visible. It
+          # would silently fall back to `stable` instead of the pin. `rust-src-dir`
+          # is the input that points it at the crate — which is also where
+          # `rust-toolchain.toml` lives, beside `.cargo/config.toml`.
+          rust-src-dir: lance-graph-java/native/lgj-abi
           # No `toolchain:` input — the action reads `rust-toolchain.toml`, so the
           # pinned version lives in exactly ONE place.
           components: rustfmt, clippy
@@ -80,6 +87,13 @@ jobs:
           path: OGAR
       - uses: actions-rust-lang/setup-rust-toolchain@v1
         with:
+          # `defaults.run.working-directory` applies to `run:` steps only, NOT
+          # to action steps: this action executes from GITHUB_WORKSPACE, where
+          # the checkout is a subdirectory and no toolchain file is visible. It
+          # would silently fall back to `stable` instead of the pin. `rust-src-dir`
+          # is the input that points it at the crate — which is also where
+          # `rust-toolchain.toml` lives, beside `.cargo/config.toml`.
+          rust-src-dir: lance-graph-java/native/lgj-abi
           components: rustfmt, clippy
       - uses: Swatinem/rust-cache@v2
         with:
@@ -114,6 +128,13 @@ jobs:
           path: OGAR
       - uses: actions-rust-lang/setup-rust-toolchain@v1
         with:
+          # `defaults.run.working-directory` applies to `run:` steps only, NOT
+          # to action steps: this action executes from GITHUB_WORKSPACE, where
+          # the checkout is a subdirectory and no toolchain file is visible. It
+          # would silently fall back to `stable` instead of the pin. `rust-src-dir`
+          # is the input that points it at the crate — which is also where
+          # `rust-toolchain.toml` lives, beside `.cargo/config.toml`.
+          rust-src-dir: lance-graph-java/native/lgj-abi
           components: rustfmt, clippy
       - uses: Swatinem/rust-cache@v2
         with: