[agent] Found by the scheduled pip / requirements.txt bug-hunt routine (ledger #309).

Summary

Since #1562 (fix for #1549), a requirements.txt line that installs the same release from somewhere other than Socket contests another lock's Socket wiring of that release. For example, a Pipfile.lock wired hosted or vendored beside a requirements.txt that says vexdemo==1.2.3 makes vex withhold the statement with patched_ref_unattributable ("… but requirements.txt resolves the same version").

That only works for the canonical name==X spelling. pip installs exactly the same upstream release for these lines, but none of them contests the wiring:

The same holds for single-version ranges that pip resolves to the wired release, such as ~=1.2.3, ==1.2.* and >=1.2.3,<=1.2.3. Those depend on what PyPI holds, so they may be a design call. The three exact spellings above are not: they can only install release X.

Impact

vex emits a not_affected statement (exit 0, with or without --no-verify), and vendor --check presumably stays green as well, for a project whose pip install -r requirements.txt ships the unpatched upstream wheel. That's the #1549 harm, reached through a different spelling. A hand-written six==1.16 (two segments) for release 1.16.0 is a common real-world form; socket-patch already treats it as equal to 1.16.0 everywhere else (#475, #604).

Repro

This uses the repo's own #1549 harness (crates/socket-patch-cli/tests/vex_pipenv_pip_common, the real CLI binary). Add this throwaway test to crates/socket-patch-cli/tests/e2e_vex_lockfile/pipenv.rs:

#[test]
#[ignore]
fn requirements_spellings_contest() {
    for (label, other) in [
        ("control", format!("{NAME}=={VERSION}\n")),
        ("===", format!("{NAME}==={VERSION}\n")),
        ("==X.0", format!("{NAME}==1.2.3.0\n")),
        ("==vX", format!("{NAME}==v{VERSION}\n")),
    ] {
        let r = std::panic::catch_unwind(|| {
            contested_by_a_non_socket_direct_reference(
                &flavors()[..1], "requirements.txt", &[(label, other.clone())]);
        });
        eprintln!("{label}: {}", if r.is_ok() { "contested" } else { "NOT contested" });
    }
}

cargo test -p socket-patch-cli --test e2e_vex_lockfile requirements_spellings_contest -- --ignored --nocapture
control: contested
===: NOT contested      # vex exit 0, "status": "not_affected" for pkg:pypi/[email protected]
==X.0: NOT contested
==vX: NOT contested

pip installs the upstream release for each spelling (real pip, six from PyPI):

for line in 'six===1.16.0' 'six==1.16.0.0' 'six==v1.16.0' 'six==1.16'; do
  echo "$line" > r.txt; python -m pip install --dry-run --no-deps -r r.txt   # pip 20.3.4: pip download --no-deps -r r.txt
done
# every cell → six-1.16.0-py2.py3-none-any.whl from files.pythonhosted.org

Expected vs actual

• Expected: CLI_CONTRACT.md, "Contested locks": a lock that "resolves the same name@version from a non-Socket source" drops the reference with patched_ref_unattributable. pip resolves ===1.2.3, ==1.2.3.0 and ==v1.2.3 to the same name@version as ==1.2.3, so each should contest the wiring the same way the canonical pin does.
• Actual: those lines are skipped as evidence. vex attests not_affected with exit 0.

OS × version

First bad: the contest itself is new in 0d741d8 (#1562), so this is a residual of that fix and not a regression. Tested on main 657fce2.

Suspect code

• crates/socket-patch-core/src/vex/discover/pypi_other.rs:347: registry_pin reads the line through utils::requirements::exact_pin (crates/socket-patch-core/src/utils/requirements.rs:542). That function returns None for === and for a version that doesn't start with a digit (v1.2.3), and it returns 1.2.3.0 verbatim.
• crates/socket-patch-core/src/vex/discover/mod.rs:924: resolved_elsewhere stores canonical_base_purl(purl), and the contest compares purl strings, so pkg:pypi/[email protected] never matches @1.2.3. The hosted rewriter already compares with utils::pep440::versions_equal (patch/redirect/requirements.rs); the contest needs the same PEP 440 equality, plus === (which pip compares as a string).

Related: #1549 / #1562 (the original contest), #1587 / #1599 (bare wheel paths, a separate residual), #475 / #604 (PEP 440-equal pins in the rewriter and in lock-only discovery).