fix(tests): require pytest when probing for a virtualenv

[BKStock]

Problem

scripts/run_tests.sh picks a virtualenv on the existence of bin/activate alone:

for candidate in "$REPO_ROOT/.venv" "$REPO_ROOT/venv" "$HOME/.hermes/hermes-agent/venv"; do
  if [ -f "$candidate/bin/activate" ]; then

A checkout carrying a .venv that was created for something else — or that never had the dev extras installed — wins the probe and the run dies with a bare No module named pytest, even when a fully populated venv/ sits right next to it. The probe order reads like a preference list but behaves as a hard first-match.

Observed on a checkout with both directories present:

$ scripts/run_tests.sh tests/agent/test_subdirectory_hints.py
Discovered 1 test files (0 tests) ...
  ║ /Users/…/.venv/bin/python: No module named pytest
=== Summary: 1 files, 0 tests passed, 0 failed (0% complete) ===

Note the summary reports 0 failed — the run looks green at a glance. The practical workaround is to call pytest directly, which is exactly what this wrapper exists to prevent.

Change

A candidate now has to prove import pytest succeeds before it is accepted, so the order expresses preference rather than first-match. Two diagnostics come with it:

• venvs that exist but lack pytest are named on stderr along with the one actually chosen, so a surprising interpreter selection is visible rather than silent
• when nothing qualifies, the error lists every path tried and the pip install -e '.[dev]' command to fix it

Verification

Same checkout, after the change:

note: skipped venv without pytest: /Users/…/.venv
      using /Users/…/venv
=== Summary: 1 files, 32 tests passed, 0 failed (100% complete) ===

Both failure paths exercised against scratch directories:

• no venv at all → error names all three probed paths
• venv present without pytest → error names it and prints the pip command

bash -n clean.

[teknium1]

Thanks for the clear reproduction and targeted test-runner fix. This is an automated hermes-sweeper review; current main already provides the requested behavior.

• scripts/run_tests.sh:54-62 only selects a POSIX venv after bin/python -c 'import pytest' succeeds, otherwise it continues probing.
• scripts/run_tests.sh:77-80 reports skipped venvs, and :93-97 reports the missing-pytest condition when no candidate qualifies.
• Commit 35b1e578621af70c5dbffd2a6fd6c534a0a1a4b7 (fix(tests): a run that collects nothing can no longer look green) added this exact guard and diagnostics; current main has since extended the same path with native Windows venv support in 3e7a11ca2e5fb9a1faa4866dad493b20fc30b0a4.

Closing as implemented on main.