ci: parallelise pytest with xdist and drop 3.15 from the blocking matrix

.github/workflows/lint.yml

@@ -74,10 +74,11 @@ jobs:
     steps:
       - uses: actions/checkout@v7
 
-      # One interpreter, not a matrix. Unit Tests and Python Compatibility sweep
-      # 3.10-3.15 because they check that the package *runs* everywhere; these
-      # tools read the source, and running them five times over would produce
-      # five copies of the same findings for five times the runner cost.
+      # One interpreter, not a matrix. Unit Tests sweeps 3.10-3.14 and Python
+      # Compatibility sweeps the same plus a schedule-only 3.15 leg, because
+      # they check that the package *runs* everywhere; these tools read the
+      # source, and running them several times over would produce several
+      # copies of the same findings for several times the runner cost.
       #
       # 3.14 specifically, matching cron-vendor.yml, because it is the newest
       # non-experimental version in the test matrix and the version the recorded

.github/workflows/python-compatibility.yml

@@ -30,28 +30,53 @@ jobs:
     # and one a three-minute test run, with nothing to tell them apart.
     name: Compat Python ${{ matrix.python-version }}
     runs-on: ubuntu-latest
-    continue-on-error: ${{ matrix.experimental == true }}
     strategy:
       fail-fast: false
       matrix:
         python-version:
+          # 3.15 deliberately excluded: ruleset 23497679's required checks
+          # only cover 3.10-3.14, so it cannot block a merge here either. Its
+          # replacement is the `compatibility-nightly` job below, which runs
+          # only on this workflow's existing weekly schedule.
           - "3.10"
           - "3.11"
           - "3.12"
           - "3.13"
           - "3.14"
-        experimental:
-          - false
-        include:
-          - python-version: "3.15"
-            experimental: true
     steps:
       - uses: actions/checkout@v7
 
       - uses: actions/setup-python@v7
         with:
           python-version: ${{ matrix.python-version }}
-          allow-prereleases: ${{ matrix.experimental }}
+
+      - name: Install package
+        run: |
+          python -m pip install -U pip setuptools wheel
+          python -m pip install -e .
+
+      - name: Verify package
+        run: |
+          python -m compileall -q pcapkit
+          python -c 'import pcapkit; print(pcapkit.__version__)'
+
+  # 3.15 is not in ruleset 23497679's required-checks list, so running it on
+  # every push/PR was queue contention with no gating signal (it was already
+  # `continue-on-error`). This job keeps early warning of a 3.15-only
+  # regression -- import and compileall only, ~14s -- without paying for it on
+  # every push: it fires solely on the schedule trigger above (line 9).
+  compatibility-nightly:
+    name: Compat Python 3.15 (scheduled)
+    if: ${{ github.event_name == 'schedule' }}
+    runs-on: ubuntu-latest
+    continue-on-error: true
+    steps:
+      - uses: actions/checkout@v7
+
+      - uses: actions/setup-python@v7
+        with:
+          python-version: "3.15"
+          allow-prereleases: true
 
       - name: Install package
         run: |

.github/workflows/unit-tests.yml

@@ -50,40 +50,49 @@ jobs:
     name: Python ${{ matrix.python-version }}
     if: ${{ inputs.gate-only != true }}
     runs-on: ubuntu-latest
-    continue-on-error: ${{ matrix.experimental == true }}
     timeout-minutes: 45
     strategy:
       fail-fast: false
       matrix:
         python-version:
+          # 3.15 deliberately excluded: ruleset 23497679's required checks
+          # only cover 3.10-3.14, so a 3.15 leg here cannot block a merge and
+          # was pure queue contention -- see python-compatibility.yml for its
+          # (non-blocking, schedule-only) replacement.
           - "3.10"
           - "3.11"
           - "3.12"
           - "3.13"
           - "3.14"
-        experimental:
-          - false
-        include:
-          - python-version: "3.15"
-            experimental: true
 
     steps:
       - uses: actions/checkout@v7
 
       - uses: actions/setup-python@v7
         with:
           python-version: ${{ matrix.python-version }}
-          allow-prereleases: ${{ matrix.experimental }}
           cache: pip
 
       - name: Install package and test dependencies
         run: |
           python -m pip install -U pip setuptools wheel
           python -m pip install -e '.[test]'
 
+      # `-n auto` resolves to whatever this runner reports, and nothing else in
+      # the log says what that was -- print it so the number `-n auto` picked
+      # is a measured fact instead of an assumption about runner size.
+      - name: Report available parallelism
+        run: |
+          nproc
+          python -c "import os; print('cpu_count', os.cpu_count())"
+
       - name: Run unit tests
+        # `--dist load` is pinned explicitly rather than left to default: a
+        # future change to xdist's own default, or someone "optimising" to
+        # `loadfile`/`loadscope`, cannot silently change how this suite is
+        # distributed.
         run: >-
-          python -m pytest -q
+          python -m pytest -q -n auto --dist load
           --ignore=tests/integration
           --ignore-glob='*_runtime.py'
           --ignore-glob='*_regression.py'
@@ -92,30 +101,24 @@ jobs:
     name: Integration Python ${{ matrix.python-version }}
     if: ${{ inputs.gate-only != true }}
     runs-on: ubuntu-latest
-    continue-on-error: ${{ matrix.experimental == true }}
     timeout-minutes: 45
     strategy:
       fail-fast: false
       matrix:
         python-version:
+          # See the `test` job above for why 3.15 is excluded here.
           - "3.10"
           - "3.11"
           - "3.12"
           - "3.13"
           - "3.14"
-        experimental:
-          - false
-        include:
-          - python-version: "3.15"
-            experimental: true
 
     steps:
       - uses: actions/checkout@v7
 
       - uses: actions/setup-python@v7
         with:
           python-version: ${{ matrix.python-version }}
-          allow-prereleases: ${{ matrix.experimental }}
           cache: pip
 
       # The Scapy extra is there for examples/generators/pcap.py and legacy.py,
@@ -152,6 +155,12 @@ jobs:
             echo "Upstream Wireshark captures were used, matching their pinned SHA-256 digests."
           fi
 
+      # See the `test` job above for why this step exists.
+      - name: Report available parallelism
+        run: |
+          nproc
+          python -c "import os; print('cpu_count', os.cpu_count())"
+
       # The ``test`` job above already ran every unit-tier test for real, on this
       # same commit. Re-running them here (a bare ``pytest -q`` used to) bought
       # no signal and cost ~21.75 minutes per Python version -- ~130 minutes per
@@ -167,7 +176,8 @@ jobs:
       # A failure to compute the selection intentionally does not fall back to
       # a bare `pytest -q` -- that would silently re-introduce the whole-suite
       # duplication this change exists to remove, with nothing in the log to
-      # say so.
+      # say so. `--dist load` is pinned explicitly; see the `test` job above
+      # for why.
       - name: Run full test suite
         shell: bash
         run: |
@@ -180,7 +190,7 @@ jobs:
             exit 1
           fi
           echo "Fixture-dependent selection: $selection"
-          python -m pytest -q $selection
+          python -m pytest -q -n auto --dist load $selection
 
   # ``CHANGELOG.md`` is generated from the newest entry under
   # ``docs/source/changelog/`` by ``util/changelog_md.py``, so it falls out of step
@@ -262,6 +272,12 @@ jobs:
             echo "Upstream Wireshark captures were used, matching their pinned SHA-256 digests."
           fi
 
+      # See the `test` job above for why this step exists.
+      - name: Report available parallelism
+        run: |
+          nproc
+          python -c "import os; print('cpu_count', os.cpu_count())"
+
       # Deliberately still the whole suite, unlike the `integration` job above:
       # this is the shipping gate's own independent re-verification (see the
       # job comment above), not the same accidental duplication #715 measured
@@ -272,6 +288,7 @@ jobs:
       # Whether `gate` should run at all on a commit the matrix already
       # covered is #715's separate item 2 ("stop the gate re-running on main
       # pushes"), a trigger-frequency question, not a selection one -- out of
-      # scope here.
+      # scope here. `--dist load` is pinned explicitly; see the `test` job
+      # above for why.
       - name: Run full test suite
-        run: python -m pytest -q
+        run: python -m pytest -q -n auto --dist load

pyproject.toml

@@ -233,6 +233,12 @@ docs = [
 ]
 test = [
     "pytest>=8",
+    # >=3.6.1, not >=3: the `shouldfail` forwarding tests/conftest.py's xdist fix
+    # depends on (xdist/remote.py:146-147) lands in 3.6.0, which PyPI has yanked,
+    # so 3.6.1 is the actual floor. Below it the fix silently reverts and
+    # test_xdist_run_reports_the_diagnostic_and_fails goes red rather than
+    # skipped, since `importlib.util.find_spec('xdist')` still succeeds.
+    "pytest-xdist>=3.6.1",
     "typing-extensions",
     # Enough of the ``vendor`` extra for a test to import a vendor crawler.
     # Without these, ``tests/vendor/test_ipx_socket_unit.py`` reports "9 skipped"