I.e. test 5564 "t5564-http-proxy.out" output may be interesting:
(during that I got asked "Password for
'http://proxuser@127.0.0.1:5564" on a prompt, after pressing enter the
tests continued to the next ones)

not ok 5 - clone can prompt for proxy password
#
#        test_when_finished "rm -rf clone" &&
#        test_config_global http.proxy http://proxuser@$HTTPD_DEST &&
#        set_askpass nobody proxpass &&
#        GIT_TRACE_CURL=$PWD/trace git clone $HTTPD_URL/smart/repo.git clone &&
#        expect_askpass pass proxuser
#

checking prerequisite: SOCKS_PROXY

mkdir -p "$TRASH_DIRECTORY/prereq-test-dir-SOCKS_PROXY" &&
(
    cd "$TRASH_DIRECTORY/prereq-test-dir-SOCKS_PROXY" &&
    test_have_prereq PERL &&
    start_socks "$TRASH_DIRECTORY/%30.sock"

)
prerequisite SOCKS_PROXY ok
expecting success of 5564.6 'clone via Unix socket':
    test_when_finished "rm -rf clone" &&
    test_config_global http.proxy "socks4://localhost$PWD/%2530.sock" && {
        {
            GIT_TRACE_CURL=$PWD/trace \
            GIT_TRACE_CURL_COMPONENTS=socks \
            git clone "$HTTPD_URL/smart/repo.git" clone 2>err &&
            grep -i "SOCKS4 request granted" trace
        } ||
        old_libcurl_error err
    }

== Info: [SOCKS] SOCKS4 request granted.

On Fri, Mar 6, 2026 at 5:14 AM Ivan Ivanov [off-list ref] wrote:

Brian, thank you very much for checking my logs: indeed, unfortunately
my system is Arch-based so we can't compare it directly with
Debian/rules. Thank you for an idea about /dev/shm , although I would
like to clarify that while it *might* be what is failing this
particular test - the causes of failure at .out files are different as
we could see by the prior 0300/0301/0302 and some future tests (could
share more logs if needed). But the external appearance of these
errors (Username/Password prompts) is similar to a user and that may
indicate some common pattern between the problems, i.e. maybe there is
some extra shell precaution needed on some systems (although I'm a bit
puzzled why my distro's packager seemingly didn't have such an issue).
I am still trying to build with skipping as few tests as possible, at
the moment I have to skip the following: t0300 t0301 t0302 t5003 t5411
t5540 t5541 t5550 t5551 t5559 t5563 t5564 (adding them to
GIT_SKIP_TESTS one-by-one, maybe there'd be more)