From 1c048444d0201efade95b277daa59416b1dd6e81 Mon Sep 17 00:00:00 2001
From: Gabriel Spadon <spadon@dal.ca>
Date: Sun, 25 Oct 2026 09:42:18 -0300
Subject: [PATCH] ci: run the floor, coverage and newest Python legs on pull
 requests

A pull request now runs Python 3.10, 3.12 and 3.14. The push to main
still runs all five supported versions, so main keeps the full verdict.
The artifact contract test now asserts that split instead of one list.
---
 .github/workflows/tests.yml        |  8 +++++++-
 tests/test_ci_artifact_contract.py | 21 ++++++++++++++++++---
 2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 6bf787c4..597153d4 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -102,7 +102,13 @@ jobs:
       # and returns every version's verdict on the first run.
       fail-fast: false
       matrix:
-        python-version: ["3.10", "3.11", "3.12", "3.13", "3.14"]
+        # A pull request runs the 3.10 floor the locks resolve for, the 3.12
+        # coverage leg and the newest interpreter; the push to main runs every
+        # version, so main still carries the full verdict. Measured over
+        # 2026-10-11..25, 11 runs averaged 13 billed minutes, 4 of them on 3.11
+        # and 3.13, and none of the 10 failed Tests runs since 2026-06 failed on
+        # 3.11 or 3.13 without the outer legs failing too.
+        python-version: ${{ github.event_name == 'pull_request' && fromJSON('["3.10", "3.12", "3.14"]') || fromJSON('["3.10", "3.11", "3.12", "3.13", "3.14"]') }}
 
     steps:
     - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
diff --git a/tests/test_ci_artifact_contract.py b/tests/test_ci_artifact_contract.py
index 9178bf64..4dde808f 100644
--- a/tests/test_ci_artifact_contract.py
+++ b/tests/test_ci_artifact_contract.py
@@ -11,6 +11,7 @@
 
 from __future__ import annotations
 
+import json
 import re
 from pathlib import Path
 from typing import Any
@@ -123,10 +124,24 @@ class TestCompatibilityMatrix:
     """Independent legs run at once, and exactly one of them owns coverage."""
 
     def test_matrix_runs_every_supported_version_concurrently(self) -> None:
-        """Serialized legs cost the sum of their wall time and hide later failures."""
-        strategy = _load_workflow(_TESTS_WORKFLOW)["jobs"]["test"]["strategy"]
+        """Serialized legs cost the sum of their wall time and hide later failures.
 
-        assert strategy["matrix"]["python-version"] == _SUPPORTED_PYTHON_VERSIONS
+        The push to main runs every supported version. A pull request runs a
+        subset, which must still hold the floor, the coverage leg and the
+        newest interpreter, so a dropped leg is one main still tests.
+        """
+        strategy = _load_workflow(_TESTS_WORKFLOW)["jobs"]["test"]["strategy"]
+        selector = re.fullmatch(
+            r"\$\{\{ github\.event_name == 'pull_request' && fromJSON\('(\[[^']*\])'\)"
+            r" \|\| fromJSON\('(\[[^']*\])'\) \}\}",
+            strategy["matrix"]["python-version"],
+        )
+
+        assert selector is not None
+        pull_request, push = (json.loads(group) for group in selector.groups())
+        assert push == _SUPPORTED_PYTHON_VERSIONS
+        assert {_SUPPORTED_PYTHON_VERSIONS[0], _COVERAGE_VERSION, _SUPPORTED_PYTHON_VERSIONS[-1]} <= set(pull_request)
+        assert set(pull_request) <= set(push)
         assert strategy["fail-fast"] is False
         assert "max-parallel" not in strategy