Action matrix: nightly shards cut by measured cost, a fresh baseline, and a determinism check (#1256)

* Action matrix: nightly shards cut by measured cost, heavy designs in slices, and a determinism check

The full matrix ran as four fixed quarters of the corpus and two of them hit the 60-minute
job limit. Now action_matrix_shard runs shard k of n (ACTION_MATRIX_SHARD=k/n), planned from
tests/action_matrix/costs.json: designs that take more than five minutes are split into slices,
and the pieces go largest first to the least loaded shard. The nightly runs 12 shards and uploads
each one's outcomes and timings; cargo xtask action-matrix --from DIR --bless records them in the
baseline and costs.json without running the matrix again. action_matrix_determinism runs a sample
twice and lists any action whose outcome changed.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

* Action matrix: costs measured on runners, 10 shards, determinism on the lighter designs

Co-Authored-By: Claude Opus 5.5 <[email protected]>

* Action matrix: baseline and costs from a full run on main, 16 shards, timeouts listed

The baseline is regenerated from the 10 shards' results of a full run on 01b1b705
(cargo xtask action-matrix --from DIR --bless): 8 new designs, 302 actions that pass now,
names that changed, and 40 actions that passed before and fail now, each listed in #1255
(22 fillets refused since #949, 4 hinge blends since #1101, 9 on the loft cut, 5 single).
costs.json now holds every design's measured time, and the nightly runs 16 shards of about
17 minutes. An action that passes in the baseline and times out is listed but not judged,
and stays passing when blessed: two runs of the same build differed only on 10 actions that
took 50-84 s against the 90 s limit.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

* Action matrix: slice heavy designs by a hash of each action's name

Slicing by index gave some slices only fillets on oracle 41 (28 slices, a multiple of the
actions per edge), three times the planned time; two shards ran past their limit.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

---------

Co-authored-by: Claude Opus 5.5 <[email protected]>

.github/workflows/ci.yml

@@ -205,16 +205,17 @@ jobs:
   action-matrix:
     # Every ordinary action on every face, edge, vertex and body of the design corpus, against
     # tests/action_matrix/baseline.json (docs/action-matrix.md). Every test run checks a sample;
-    # the whole matrix runs nightly (or by hand), a quarter per job.
-    name: Action matrix (${{ matrix.part }}/4)
+    # the whole matrix runs nightly (or by hand) in shards of about equal cost, cut by
+    # tests/action_matrix/costs.json. Keep SHARDS in step with the matrix below.
+    name: Action matrix (${{ matrix.shard }}/16)
     needs: build-tests
     if: github.event_name == 'schedule' || github.event_name == 'workflow_dispatch'
     runs-on: ubuntu-24.04
-    timeout-minutes: 60
+    timeout-minutes: 55
     strategy:
       fail-fast: false
       matrix:
-        part: [1, 2, 3, 4]
+        shard: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
       - uses: taiki-e/install-action@1168f6810a3cb30a3514bf5756a3b7f0422c6df8 # v2.87.28
@@ -223,12 +224,48 @@ jobs:
       - uses: actions/download-artifact@9000827ccba6bdab643e8b6fd33ac0654aef8333 # v8.0.2
         with:
           name: nextest-archive
-      - name: Run a quarter of the matrix
+      - name: Run one shard of the matrix
+        # A step limit below the job's, so the outcomes so far are still uploaded.
+        timeout-minutes: 45
         env:
-          PART: ${{ matrix.part }}
+          SHARDS: 16
+          SHARD: ${{ matrix.shard }}
+          OUT: ${{ github.workspace }}/action-matrix
+        run: |
+          mkdir -p "$OUT"
+          export ACTION_MATRIX_SHARD="$SHARD/$SHARDS" ACTION_MATRIX_RESULTS="$OUT/results-$SHARD.json" \
+            ACTION_MATRIX_TIMINGS="$OUT/timings-$SHARD.jsonl" ACTION_MATRIX_WORKDIR="$OUT/raw-$SHARD"
+          cargo nextest run --archive-file tests.tar.zst --workspace-remap . --extract-to . --extract-overwrite \
+            --profile ci --success-output final --run-ignored only -E "binary(action_matrix) & test(=action_matrix_shard)"
+      - name: Upload the outcomes and timings
+        # `cargo xtask action-matrix --from DIR --bless` (with every shard's files in DIR)
+        # records them in the baseline and costs.json.
+        if: always()
+        uses: actions/upload-artifact@cf430e030ddbb5b0abf93d22962f4752f3646cd9 # v7.0.2
+        with:
+          name: action-matrix-${{ matrix.shard }}
+          path: action-matrix
+          retention-days: 14
+
+  action-matrix-determinism:
+    # A sample of the matrix run twice on one runner: every action must come out the same.
+    name: Action matrix determinism
+    needs: build-tests
+    if: github.event_name == 'schedule' || github.event_name == 'workflow_dispatch'
+    runs-on: ubuntu-24.04
+    timeout-minutes: 45
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: taiki-e/install-action@1168f6810a3cb30a3514bf5756a3b7f0422c6df8 # v2.87.28
+        with:
+          tool: cargo-nextest
+      - uses: actions/download-artifact@9000827ccba6bdab643e8b6fd33ac0654aef8333 # v8.0.2
+        with:
+          name: nextest-archive
+      - name: Run a sample twice
         run: |
           cargo nextest run --archive-file tests.tar.zst --workspace-remap . --extract-to . --extract-overwrite \
-            --profile ci --run-ignored only -E "binary(action_matrix) & test(=action_matrix_full_$PART)"
+            --profile ci --success-output final --run-ignored only -E "binary(action_matrix) & test(=action_matrix_determinism)"
 
   doc-tests:
     name: Doc tests