diff --git a/astropy_integration/dashboard.py b/astropy_integration/dashboard.py
index 790d299..7775edb 100644
--- a/astropy_integration/dashboard.py
+++ b/astropy_integration/dashboard.py
@@ -68,6 +68,7 @@ def _variant_meta(variant, python, data):
         "python_version": data.get("python_version") or python,
         "started_at": data["started_at"],
         "finished_at": data["finished_at"],
+        "installed_deps": data.get("installed_deps") or {},
     }
 
 
diff --git a/astropy_integration/run.py b/astropy_integration/run.py
index b0dda3c..49cc0d2 100644
--- a/astropy_integration/run.py
+++ b/astropy_integration/run.py
@@ -2,7 +2,9 @@
 
 Creates a single shared venv, installs astropy first then each package
 from packages.yaml in order, recording per-package install outcome
-(installed / skipped / install-fail / no-spec). Then runs
+(installed / skipped / install-fail / no-spec). Each install is
+constrained so it can never downgrade a package already in the venv;
+a package needing an older version is reported as skipped. Then runs
 `pytest --pyargs <module>` for each successfully-installed package.
 Writes results/<variant>__<python>.json with the full venv freeze and
 per-package data.
@@ -223,6 +225,29 @@ def _freeze(python):
     return out
 
 
+def _write_no_downgrade_constraints(python, path):
+    """Pin every installed package to '>=' its current version.
+
+    Passed as a uv `--constraint` file to later installs so a new package
+    can pull its deps forward but never downgrade what the shared venv
+    already has; a package that genuinely needs an older version then
+    shows up as a resolver conflict (skipped) instead of silently
+    poisoning the venv for everything tested afterwards.
+    """
+    frozen = _freeze(python)
+    lines = []
+    for name, ver in sorted(frozen.items()):
+        try:
+            # Drop any PEP 440 local-version segment (e.g. the '+g1a2b3c4'
+            # on astropy/pyerfa nightly wheels): uv rejects a '>=' specifier
+            # with a local segment and would fail to parse the whole file.
+            public = Version(ver).public
+        except InvalidVersion:
+            continue
+        lines.append(f"{name}>={public}")
+    Path(path).write_text("\n".join(lines) + ("\n" if lines else ""))
+
+
 def _load_packages(path):
     raw = yaml.safe_load(Path(path).read_text()) or {}
     return list(raw.get("packages", []))
@@ -313,6 +338,7 @@ def run_variant(variant, python_version, packages, repo_root, results_dir, timeo
             return result, out_path
         python = os.path.join(venv, "bin", "python")
         result["python_version"] = _venv_python_version(python)
+        constraints_path = os.path.join(tmpdir, "no-downgrade-constraints.txt")
 
         common = ["uv", "pip", "install", "--python", python, "-q"]
         for url in astropy["extra_index_urls"]:
@@ -339,6 +365,7 @@ def run_variant(variant, python_version, packages, repo_root, results_dir, timeo
         result["astropy"]["version"] = (
             _pkg_version(python, "astropy") or result["astropy"]["version"]
         )
+        _write_no_downgrade_constraints(python, constraints_path)
 
         installed_pkgs = []
         for pkg, install_spec, target_version in pkg_specs:
@@ -364,13 +391,18 @@ def run_variant(variant, python_version, packages, repo_root, results_dir, timeo
                 continue
 
             print(f"\nInstalling {pkg['pypi_name']}...")
-            install_cmd = common + [install_spec] + (pkg.get("extra_deps") or [])
+            install_cmd = (
+                common
+                + ["--constraint", constraints_path, install_spec]
+                + (pkg.get("extra_deps") or [])
+            )
             rc, err = _run_install(install_cmd, timeouts["install"])
             if rc == 0:
                 entry["install_status"] = status.INSTALLED
                 entry["resolved_version"] = _pkg_version(python, pkg["pypi_name"])
                 print(f"  installed at {entry['resolved_version']}")
                 installed_pkgs.append((pkg, entry))
+                _write_no_downgrade_constraints(python, constraints_path)
             else:
                 entry["install_error"] = err
                 if _resolver_conflict(err):
@@ -467,12 +499,20 @@ def run(args):
     # instead of buffering until the script exits.
     sys.stdout.reconfigure(line_buffering=True)
 
-    packages = _load_packages(args.config)
+    all_packages = _load_packages(args.config)
+    packages = all_packages
     if args.tiers:
         wanted_tiers = {t.strip() for t in args.tiers.split(",") if t.strip()}
         packages = [p for p in packages if p.get("tier", "coordinated") in wanted_tiers]
     if args.packages:
         wanted = {n.strip() for n in args.packages.split(",") if n.strip()}
+        known = {p["pypi_name"] for p in all_packages}
+        unknown = wanted - known
+        if unknown:
+            sys.exit(
+                f"Unknown package name(s): {', '.join(sorted(unknown))}. "
+                f"Valid names are the pypi_name entries in {args.config}."
+            )
         packages = [p for p in packages if p["pypi_name"] in wanted]
     packages = _install_order(packages)
 
diff --git a/astropy_integration/templates/_style.css b/astropy_integration/templates/_style.css
index 8fb1755..47940ec 100644
--- a/astropy_integration/templates/_style.css
+++ b/astropy_integration/templates/_style.css
@@ -32,3 +32,22 @@ details summary { cursor: pointer; padding: 4px 0; font-weight: 600; }
 nav { margin-bottom: 1.5em; font-size: 0.9em; }
 .legend { font-size: 0.85em; color: #6a737d; margin-top: 1em; }
 .legend .pill { margin: 0 0.3em; }
+
+@media (prefers-color-scheme: dark) {
+  body { background: #0d1117; color: #c9d1d9; }
+  a { color: #58a6ff; }
+  th, td { border-color: #30363d; }
+  th { background: #161b22; }
+  th.python-group { border-bottom-color: #484f58; }
+  .banner { background: #2b1d00; border-color: #6e5500; }
+  tr.tier-header th { background: #161b22; color: #8b949e; }
+  .meta dl { color: #8b949e; }
+  .matrix tr:hover td { background: #161b22; }
+  .pill.pass        { background: #0a3a17; color: #3fb950; }
+  .pill.fail        { background: #4a1216; color: #f85149; }
+  .pill.no-tests    { background: #21262d; color: #8b949e; }
+  .pill.skipped     { background: #21262d; color: #8b949e; }
+  .pill.install-fail{ background: #3d2900; color: #e3b341; }
+  .pill.timeout     { background: #261c4a; color: #a371f7; }
+  .pill.missing     { background: #161b22; color: #6e7681; }
+}
diff --git a/astropy_integration/templates/index.html b/astropy_integration/templates/index.html
index 3602b77..de253e3 100644
--- a/astropy_integration/templates/index.html
+++ b/astropy_integration/templates/index.html
@@ -96,6 +96,23 @@ <h3>Test output</h3>
 <p class="legend">No failures &mdash; every package passed in every variant that ran.</p>
 {% endif %}
 
+{% if variants_meta|selectattr("installed_deps")|list %}
+<h2>Installed packages</h2>
+<p class="legend">Full <code>uv pip freeze</code> of the shared venv for each variant that ran.</p>
+{% for v in variants_meta %}
+{% if v.installed_deps %}
+<details>
+  <summary>
+    <code>{{ v.variant }}</code> / Python <code>{{ v.python }}</code>
+    <small style="color:#6a737d">({{ v.installed_deps|length }} packages)</small>
+  </summary>
+  <pre>{% for name, ver in v.installed_deps|dictsort %}{{ name }}=={{ ver }}
+{% endfor %}</pre>
+</details>
+{% endif %}
+{% endfor %}
+{% endif %}
+
 <script>
 function openTarget() {
   const id = location.hash.slice(1);
diff --git a/conftest.py b/conftest.py
index 5180a3f..0c55230 100644
--- a/conftest.py
+++ b/conftest.py
@@ -1,15 +1,25 @@
-"""Repo-level pytest plugin used during PR-preview runs.
+"""Repo-level pytest plugin, auto-discovered because the runner invokes
+every `pytest --pyargs <module>` with cwd set to the repo root.
 
-When the env var `PYTEST_LIMIT_N` is set to a positive integer, pytest
-collects normally and then truncates the test list to the first N
-items. This lets the PR matrix surface a fast smoke signal per
-package (typically 10 tests each) without per-package configuration.
+Two jobs:
 
-Discovered automatically by pytest because cwd is the repo root for
-every `pytest --pyargs <module>` invocation in the runner.
+1. PR-preview smoke runs: when the env var `PYTEST_LIMIT_N` is set to a
+   positive integer, pytest collects normally and then truncates the
+   test list to the first N items. This lets the PR matrix surface a
+   fast smoke signal per package (typically 10 tests each) without
+   per-package configuration.
+
+2. Supply shared test fixtures that a package defines in its own
+   repo-root conftest.py but does not ship in the installed wheel.
+   `pytest --pyargs` collects from site-packages, so such fixtures are
+   otherwise missing and their tests error at setup. Currently:
+   `tmp_cwd` (astroquery).
 """
 
 import os
+from pathlib import Path
+
+import pytest
 
 
 def pytest_collection_modifyitems(config, items):
@@ -22,3 +32,22 @@ def pytest_collection_modifyitems(config, items):
         return
     if n > 0 and len(items) > n:
         del items[n:]
+
+
+@pytest.fixture(scope="function")
+def tmp_cwd(tmp_path):
+    """astroquery shim: run the test in a pristine temp working directory.
+
+    Exists solely for astroquery, which defines this fixture in its
+    repo-root conftest.py. That file is not part of the installed
+    package, so the fixture is missing under `pytest --pyargs
+    astroquery` and the esa/utils, esa/iso and esa/xmm_newton download
+    tests error out at setup. Remove this if astroquery ever ships the
+    fixture inside the package.
+    """
+    old_dir = Path.cwd()
+    os.chdir(tmp_path)
+    try:
+        yield tmp_path
+    finally:
+        os.chdir(old_dir)
diff --git a/packages.yaml b/packages.yaml
index cc49902..1614e6b 100644
--- a/packages.yaml
+++ b/packages.yaml
@@ -38,6 +38,11 @@ packages:
     module: astroquery
     repo_url: https://github.com/astropy/astroquery.git
     install_extras: [test, all]
+    # test_raises_deprecation_warning uses pytest.raises() on a warning,
+    # which only works under astroquery's own filterwarnings=error config;
+    # that setup.cfg config is not picked up when running --pyargs from
+    # the harness rootdir, so the test cannot pass here.
+    pytest_args: ["-k", "not test_raises_deprecation_warning"]
 
   - pypi_name: ccdproc
     tier: coordinated
@@ -104,10 +109,11 @@ packages:
     module: astroalign
     repo_url: https://github.com/quatrope/astroalign.git
 
-  - pypi_name: astroML
-    tier: affiliated
-    module: astroML
-    repo_url: https://github.com/astroML/astroML.git
+  # astroML is no longer maintained, so it is excluded from the matrix.
+  # - pypi_name: astroML
+  #   tier: affiliated
+  #   module: astroML
+  #   repo_url: https://github.com/astroML/astroML.git
 
   - pypi_name: astroplan
     tier: affiliated