ci: reuse portable Turbo outputs across verification runs

.github/actions/portable-build-cache/action.yml

@@ -0,0 +1,40 @@
+name: Portable build cache
+description: Reuse Turbo build outputs without serializing verification jobs.
+inputs:
+  save:
+    description: Save newly built outputs after the job succeeds.
+    default: "false"
+runs:
+  using: composite
+  steps:
+    - name: Resolve portable build task hashes
+      id: plan
+      shell: bash
+      env:
+        BUILD_CACHE_PREFIX: rea-portable-build-v1-${{ runner.os }}-${{ runner.arch }}-${{ hashFiles('.npmrc') }}
+      run: |
+        npm run --silent test:prepare -- --dry=json |
+          node --input-type=module -e '
+            import { createHash } from "node:crypto";
+            import { readFileSync } from "node:fs";
+            const { tasks } = JSON.parse(readFileSync(0, "utf8"));
+            const hashes = tasks.map(({ taskId, hash }) => {
+              if (typeof hash !== "string")
+                throw new Error(`Build task ${taskId} must have an eager Turbo hash`);
+              return `${taskId}:${hash}`;
+            }).sort();
+            const hash = createHash("sha256").update(hashes.join("\n")).digest("hex");
+            console.log(`key=${process.env.BUILD_CACHE_PREFIX}-${hash}`);
+          ' >> "$GITHUB_OUTPUT"
+    - name: Restore portable build outputs
+      if: inputs.save != 'true'
+      uses: actions/cache/restore@v4
+      with:
+        path: .turbo/cache/
+        key: ${{ steps.plan.outputs.key }}
+    - name: Restore and save portable build outputs
+      if: inputs.save == 'true'
+      uses: actions/cache@v4
+      with:
+        path: .turbo/cache/
+        key: ${{ steps.plan.outputs.key }}

.github/workflows/ci.yml

@@ -145,6 +145,10 @@ jobs:
           node-version-file: .nvmrc
           cache: npm
       - run: npm ci
+      - name: Reuse portable build outputs across runs
+        uses: ./.github/actions/portable-build-cache
+        with:
+          save: "true"
       - run: npm run test:prepare
       - name: Find successful default-branch timing history
         id: history

.github/workflows/real-binary-layout.yml

@@ -32,6 +32,7 @@ jobs:
           node-version-file: .nvmrc
           cache: npm
       - run: npm ci
+      - uses: ./.github/actions/portable-build-cache
       - name: Acquire exact upstream libraries in an isolated runner environment
         shell: bash
         run: |

.github/workflows/real-browser.yml

@@ -22,9 +22,10 @@ jobs:
       - uses: actions/checkout@v4
       - uses: actions/setup-node@v4
         with:
-          node-version: 24
+          node-version-file: .nvmrc
           cache: npm
       - run: npm ci
+      - uses: ./.github/actions/portable-build-cache
       - run: npm run verify:browser
         env:
           REA_BROWSER_EXECUTABLE: /usr/bin/google-chrome

.github/workflows/real-evm-interface.yml

@@ -26,6 +26,7 @@ jobs:
           node-version-file: .nvmrc
           cache: npm
       - run: npm ci
+      - uses: ./.github/actions/portable-build-cache
       - name: Acquire unchanged fixture compiler in isolated runner storage
         shell: bash
         run: |

.github/workflows/real-javascript-recovery.yml

@@ -24,9 +24,10 @@ jobs:
       - uses: actions/checkout@v4
       - uses: actions/setup-node@v4
         with:
-          node-version: 24
+          node-version-file: .nvmrc
           cache: npm
       - run: npm ci
+      - uses: ./.github/actions/portable-build-cache
       - name: Fetch pinned Wakaru release into the job workspace
         shell: bash
         run: |

.github/workflows/real-recorded-crash.yml

@@ -29,6 +29,7 @@ jobs:
           node-version-file: .nvmrc
           cache: npm
       - run: npm ci
+      - uses: ./.github/actions/portable-build-cache
       - name: Install GDB on the disposable CI runner
         shell: bash
         run: |

.github/workflows/real-web-network-captures.yml

@@ -28,6 +28,7 @@ jobs:
       - name: Use pinned package manager
         run: npm install --global [email protected]
       - run: npm ci
+      - uses: ./.github/actions/portable-build-cache
       - name: Acquire fixed upstream native profile in runner temporary storage
         shell: bash
         run: |

.github/workflows/real-web-runtime.yml

@@ -17,9 +17,10 @@ jobs:
       - uses: actions/checkout@v4
       - uses: actions/setup-node@v4
         with:
-          node-version: 24
+          node-version-file: .nvmrc
           cache: npm
       - run: npm ci
+      - uses: ./.github/actions/portable-build-cache
       - run: npm run verify:browser:runtime
         env:
           REA_BROWSER_EXECUTABLE: /usr/bin/google-chrome

.github/workflows/real-web-source-map.yml

@@ -17,9 +17,10 @@ jobs:
       - uses: actions/checkout@v4
       - uses: actions/setup-node@v4
         with:
-          node-version: 24
+          node-version-file: .nvmrc
           cache: npm
       - run: npm ci
+      - uses: ./.github/actions/portable-build-cache
       - name: Install the pinned compiler into an isolated fixture directory
         run: npm install --prefix "$RUNNER_TEMP/rea-web-source-map-compiler" --no-audit --no-fund --package-lock=false [email protected]
       - run: npm run verify:browser:source-maps

docs/testing.md

@@ -1015,6 +1015,13 @@ summary. Static checks, documentation, build, package verification, and
 real-system lanes remain separate jobs so one kind of evidence cannot stand in
 for another.
 
+The build job saves portable Turbo outputs across runs. Eight Linux real-system
+lanes restore this cache without waiting for the build job. The shared action
+derives its key from `test:prepare --dry=json` task hashes, runner OS and
+architecture, and `.npmrc`; test-only changes can reuse compiled outputs. Every
+build and verification command still runs, so Turbo checks task inputs and
+rebuilds misses. There is no prefix fallback to accumulate older build outputs.
+
 Native package jobs reuse the same workflow's Turbo cache for portable compiled
 JavaScript, skills, and catalogs. They retain the normal build and prepack
 commands, which restore matching outputs or rebuild on a cache miss. Native