fix(hydrate): gate posix_fadvise to Linux/Android, not cfg(unix)

.claude/board/ISSUES.md

@@ -1,3 +1,47 @@
+## ISS-NO-NON-LINUX-TARGET (2026-09-06) — OPEN
+
+**Neither filed issue covers the defect that opened this one, and the difference
+is the generalization.** `crates/lance-graph-hydrate/src/release.rs` gated three
+sites `#[cfg(unix)]` and called `libc::posix_fadvise` / `libc::POSIX_FADV_DONTNEED`
+inside them. `posix_fadvise` is **Linux/Android, not POSIX-universal** — Apple's
+libc does not declare it — so the crate fails to compile on macOS with
+`error[E0425]: cannot find function 'posix_fadvise' in crate 'libc'`. `cfg(unix)`
+reads as "has fadvise" and is not.
+
+Why the two existing issues miss it:
+
+- `ISS-NO-AARCH64-RUNNER` is about target **arch**. This is target **OS**: the cfg
+  selection was proved two-sidedly on the pinned 1.98.1 toolchain with a `#![no_std]`
+  rustc probe — `x86_64-apple-darwin` excludes the Linux arm, `x86_64-unknown-linux-gnu`
+  selects it. An x86 macOS runner would have caught this; an aarch64 *Linux* one
+  would not.
+- `ISS-EXCLUDED-CRATES-UNBUILT` is about the **member list**. `lance-graph-hydrate`
+  is a workspace member, compiled and linted by CI on every PR. The crate list was
+  never the gap here.
+
+**The accurate statement is the union, not either half:** CI compiles exactly ONE
+`(target_os, target_arch, crate-list)` tuple — `(linux, x86_64, members)`. Every
+`cfg` block outside it is text the parser skips. The three defects found this week
+each fall in a different one of those three axes, which is why fixing one axis would
+not have caught the other two.
+
+**Found the same way as the other two:** by q2's newly-ungated `macos-latest` job —
+a downstream consumer's CI doing this repo's job, for the third time in one week.
+Nothing in this repo's own CI was capable of seeing it.
+
+**Fixed here** (the point repair): the three sites are gated
+`#[cfg(any(target_os = "linux", target_os = "android"))]` with a fallback arm for
+macOS/BSD, and the doc comment records the rule — *widen this gate only to targets
+whose libc actually declares the call*. 39/39 crate tests green on Linux.
+
+**Not fixed here:** the axis. A `runs-on: macos-latest` job, or a cheap
+`cargo check --target x86_64-apple-darwin` on the existing x86 runners, is a CI
+policy change and an operator call. Note the cheap form needs
+`rustup target add --toolchain 1.98.1 <target>` — installing a target for the
+DEFAULT toolchain while the repo pins 1.98.1 produces a `can't find crate for 'core'`
+that reads like a broken probe rather than a missing std; that cost a turn this
+session.
+
 ## ISS-NO-AARCH64-RUNNER (2026-09-06) — OPEN
 
 **Every `#[cfg(target_arch = "aarch64")]` block in this repo is unverified, because

crates/lance-graph-hydrate/src/release.rs

@@ -22,7 +22,7 @@ use std::path::{Path, PathBuf};
 /// in the page cache. A no-op hint — `POSIX_FADV_DONTNEED` can only be
 /// declined, never fail unsafely, so the return value is intentionally not
 /// surfaced.
-#[cfg(unix)]
+#[cfg(any(target_os = "linux", target_os = "android"))]
 fn advise_dontneed_file(f: &fs::File) {
     use std::os::unix::io::AsRawFd;
     let fd = f.as_raw_fd();
@@ -36,9 +36,9 @@ fn advise_dontneed_file(f: &fs::File) {
     }
 }
 
-/// unix: open the file and advise DONTNEED; only counts on successful open
-/// (matches the prior behavior this council hardened).
-#[cfg(unix)]
+/// linux/android: open the file and advise DONTNEED; only counts on successful
+/// open (matches the prior behavior this council hardened).
+#[cfg(any(target_os = "linux", target_os = "android"))]
 fn release_one_file(path: &Path) -> bool {
     if let Ok(f) = fs::File::open(path) {
         advise_dontneed_file(&f);
@@ -48,10 +48,19 @@ fn release_one_file(path: &Path) -> bool {
     }
 }
 
-/// non-unix: there is no portable fadvise equivalent, so opening the file
+/// Everywhere else: there is no `posix_fadvise` equivalent, so opening the file
 /// would be pure syscall cost for zero benefit — a council-found waste
 /// (2026-08-17). Count the entry without opening it.
-#[cfg(not(unix))]
+///
+/// **This arm covers macOS and the other BSDs, not just non-unix.** The gate
+/// was `cfg(unix)` until 2026-09-06, which reads as "has fadvise" but is not:
+/// `posix_fadvise` is a Linux (and Android) interface that Apple's libc does
+/// not provide, so `libc` does not declare it for `*-apple-*` and the crate
+/// failed to compile there with `E0425: cannot find function posix_fadvise`.
+/// Nothing caught it because every lance-graph CI runner is `ubuntu-*`; it
+/// surfaced only through a downstream consumer's macOS job. Widen this gate
+/// only to targets whose libc actually declares the call.
+#[cfg(not(any(target_os = "linux", target_os = "android")))]
 fn release_one_file(_path: &Path) -> bool {
     true
 }