feat(ci): benchmark a startup floor alongside every shard

.github/workflows/ci.yml

@@ -507,6 +507,15 @@ jobs:
           fi
           mkdir -p shard-fixtures
           cp -r "bench-fixtures/$FIXTURE" shard-fixtures/
+          # The floor rides along in every shard, never as a shard of its own:
+          # startup is a property of this runner, and shards land on different
+          # machines, so subtracting one shard's floor from another's total
+          # would measure the hardware gap instead of the work.
+          if [[ ! -d "bench-fixtures/floor" ]]; then
+            echo "::error::generated fixtures contain no 'floor'"
+            exit 1
+          fi
+          cp -r bench-fixtures/floor shard-fixtures/
       - uses: actions/setup-node@48b55a011bda9f5d6aeb4c2d9c7362e8dae4041e # v6
         with:
           node-version: '24'
@@ -527,7 +536,7 @@ jobs:
           key: bench-npm-cache-${{ hashFiles('.github/workflows/ci.yml', 'benchmarks/fixtures/definitions/*.json') }}
           restore-keys: |
             bench-npm-cache-
-      - uses: FerrLabs/Benchmarks@3d9a4fa078bb94993b8a7f78633aad2a7c740feb # v5 + Fixtures v1.1.1 + sharding + cold-cache benchmark
+      - uses: FerrLabs/Benchmarks@e1237b5e267fe331ea7dd78bbd313c3bf0ff2c72 # v5 + Fixtures v1.1.1 + sharding + cold-cache + startup/work split
         with:
           type: full
           definitions: benchmarks/fixtures/definitions
@@ -567,7 +576,7 @@ jobs:
         with:
           pattern: bench-partial-*
           path: partials/
-      - uses: FerrLabs/Benchmarks@3d9a4fa078bb94993b8a7f78633aad2a7c740feb # v5 + Fixtures v1.1.1 + sharding + cold-cache benchmark
+      - uses: FerrLabs/Benchmarks@e1237b5e267fe331ea7dd78bbd313c3bf0ff2c72 # v5 + Fixtures v1.1.1 + sharding + cold-cache + startup/work split
         with:
           type: full
           definitions: benchmarks/fixtures/definitions

benchmarks/fixtures/definitions/floor.json

@@ -0,0 +1,25 @@
+{
+  "meta": {
+    "name": "floor",
+    "description": "Startup floor: 1 package, 1 commit since the last tag. The smallest real job each tool can be given, so its median is the fixed cost of invoking the tool at all.",
+    "default_branch": "main"
+  },
+  "generate": {
+    "packages": 1,
+    "commits": 1
+  },
+  "tool_configs": {
+    "ferrflow": {
+      "ferrflow.json": "{\"package\":[{\"name\":\"myapp\",\"path\":\".\",\"changelog\":\"CHANGELOG.md\",\"versioned_files\":[{\"path\":\"package.json\",\"format\":\"json\"}]}]}"
+    },
+    "changesets": {
+      "package.json": "{\"name\":\"myapp\",\"version\":\"0.1.0\",\"private\":true}",
+      ".changeset/config.json": "{\"$schema\":\"https://unpkg.com/@changesets/config@3.0.0/schema.json\",\"changelog\":\"@changesets/cli/changelog\",\"commit\":false,\"fixed\":[],\"linked\":[],\"access\":\"restricted\",\"baseBranch\":\"main\",\"updateInternalDependencies\":\"patch\",\"ignore\":[]}",
+      ".changeset/initial.md": "---\n\"myapp\": patch\n---\n\nseed changeset so `changesets status` exits 0 on this single-package fixture\n"
+    },
+    "semantic-release": {
+      "package.json": "{\"name\":\"myapp\",\"version\":\"0.1.0\",\"private\":true}",
+      ".releaserc.json": "{\"branches\":[\"main\"],\"plugins\":[\"@semantic-release/commit-analyzer\",\"@semantic-release/release-notes-generator\"]}"
+    }
+  }
+}