fix(ingest): finish the non-regular-file guards left out of 3.7.1 (#2221)

The #2221 fix reached develop through #2228 at an earlier revision of the
branch, so three guards and their tests did not come with it. One of the
three is a regression the gate that did land introduced.

sweep_directory: the new gate probes the file type with f.stat() inside a
try, and its except OSError printed SKIP and continued. A dangling symlink,
a symlink loop and a file unlinked between rglob and the gate all raise
there. Before the gate existed each of them reached sweep(), raised, and was
appended to failures — so the gate turned "could not read this transcript"
into a silent skip and a successful exit. A probe that FAILS is an error,
not a benign file type: log it, print WARNING, book it in failures. A probe
that succeeds and reports a non-regular file still skips silently.

_parse_gradle: the is_file() gate sat in front of the try whose except
OSError the parser already had, so a manifest under a directory with r but
no x raised PermissionError out of a call that used to answer "no manifest
name". The gate moves inside that try. _collect_manifest_names stats with
os.path.isfile, which reports instead of raising, matching the parsers it
guards.

split_file: the type gate in main() covers the files the glob listed, but
split_file builds its output names itself, so a pre-existing FIFO at one of
them wedged write_text in the kernel waiting for a reader. Output names that
are anything but a regular file are skipped.

That gate asks os.path.lexists, not os.path.exists. exists() follows the
link, so a DANGLING symlink at an output name reads as "nothing there" and
the write goes through it, creating the target — a chunk landing wherever
the link points rather than in the output directory. Measured: the two calls
differ on that one case and agree on every other (regular file, symlink to a
file, missing name, FIFO, symlink to FIFO, directory).

test_gather_origin_samples_survives_an_unreadable_directory broke under root
rather than passing vacuously: CAP_DAC_OVERRIDE walks into the 0o444
directory, the walled-off file stays readable, and the count assertion sees
two samples instead of one. It now carries the same needs_unprivileged_posix
gate as the three new permission tests.

miner._read_text_no_follow: comment fix only. F_SETLEASE on a FIFO fails
EINVAL, not ENXIO — measured on Linux 6.18 / glibc 2.39. The code branches
on EAGAIN and is unaffected.

Author: mvalentsev

CHANGELOG.md

@@ -8,6 +8,12 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 
 ## [Unreleased]
 
+### Bug Fixes
+
+- **`sweep` books a failed `stat` as a failure again.** The non-regular-file gate added in 3.7.1 reads `stat.S_ISREG(f.stat().st_mode)` inside a `try`, and its `except OSError` printed `SKIP` and moved on. A dangling symlink, a symlink loop and a file unlinked between `rglob` and the gate all raise there, and before the gate existed every one of them reached `sweep()` and was booked in `failures` — so `sweep` went from reporting a transcript it could not read to reporting success. A failed probe is now an error, not a benign file type: it is logged, printed as `WARNING`, and appended to `failures`, while a probe that succeeds and says "not regular" still skips silently. (#2221)
+- **`mempalace init` no longer tracebacks on a directory it cannot enter.** `_parse_gradle`'s `is_file()` gate sat in front of the `try` that the parser's own `except OSError` provides, so a manifest under a directory with `r` but no `x` raised `PermissionError` out of a call that used to answer "no manifest name". The gate moved inside that `try`, and `_collect_manifest_names` stats through `os.path.isfile`, which reports rather than raises. (#2221)
+- **`split` no longer blocks on a FIFO at its own output name, nor writes through a broken link.** The type gate in `main` covers the files the glob listed; `split_file` builds its output names itself, so a pre-existing named pipe at one of them wedged `write_text` in the kernel waiting for a reader. The check asks about the link itself rather than its target, because a dangling symlink at an output name reads as "nothing there" and `write_text` would create the target — landing a chunk outside the output directory. Output names that are anything but a regular file are now skipped with a `SKIP` line. (#2221)
+
 ---
 
 ## [3.8.0] — 2026-08-20