diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 8e332e79c..846de4735 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -34,6 +34,7 @@ jobs:
     name: Classify changes
     runs-on: ubuntu-latest
     outputs:
+      code: ${{ steps.package.outputs.required }}
       package: ${{ steps.package.outputs.required }}
     steps:
       - uses: actions/checkout@v4
@@ -60,7 +61,34 @@ jobs:
 
   static:
     name: Static checks
+    needs: changes
+    if: ${{ always() }}
     runs-on: ubuntu-latest
+    steps:
+      - name: Require successful change classification
+        env:
+          CHANGES_RESULT: ${{ needs.changes.result }}
+        run: test "${CHANGES_RESULT}" = "success"
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version-file: .nvmrc
+          cache: npm
+      - run: npm ci
+      - if: github.event_name == 'push' || needs.changes.outputs.code == 'true'
+        run: npm run check:ci
+      - if: github.event_name == 'pull_request' && needs.changes.outputs.code != 'true'
+        run: npm run format:check
+
+  test-shard:
+    name: Test shard (${{ matrix.shard }})
+    needs: changes
+    if: github.event_name == 'push' || needs.changes.outputs.code == 'true'
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        shard: [1/2, 2/2]
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-node@v4
@@ -68,24 +96,54 @@ jobs:
           node-version-file: .nvmrc
           cache: npm
       - run: npm ci
-      - run: npm run check:ci
+      - run: npm run test:ci:shard -- --shard=${{ matrix.shard }}
+      - uses: actions/upload-artifact@v4
+        if: ${{ !cancelled() }}
+        with:
+          name: vitest-report-${{ strategy.job-index }}
+          path: .vitest-reports/*
+          include-hidden-files: true
+          if-no-files-found: error
+          overwrite: true
+          retention-days: 1
 
   test:
     name: Test (coverage + timing)
+    needs: [changes, test-shard]
+    if: ${{ always() }}
     runs-on: ubuntu-latest
     steps:
+      - name: Require successful test shards
+        env:
+          CHANGES_RESULT: ${{ needs.changes.result }}
+          CODE_REQUIRED: ${{ needs.changes.outputs.code }}
+          SHARD_RESULT: ${{ needs.test-shard.result }}
+        run: |
+          test "${CHANGES_RESULT}" = "success"
+          test "${CODE_REQUIRED}" != "true" || test "${SHARD_RESULT}" = "success"
       - uses: actions/checkout@v4
+        if: needs.changes.outputs.code == 'true' && success()
       - uses: actions/setup-node@v4
+        if: needs.changes.outputs.code == 'true' && success()
         with:
           node-version-file: .nvmrc
           cache: npm
-      - run: npm ci
-      - run: npm run test:ci
+      - if: needs.changes.outputs.code == 'true' && success()
+        run: npm ci
+      - uses: actions/download-artifact@v4
+        if: needs.changes.outputs.code == 'true' && success()
+        with:
+          path: .vitest-reports
+          pattern: vitest-report-*
+          merge-multiple: true
+      - if: needs.changes.outputs.code == 'true' && success()
+        run: npm run test:ci:merge
       - uses: actions/upload-artifact@v4
-        if: always()
+        if: needs.changes.outputs.code == 'true' && always()
         with:
           name: test-results
           path: test-results.xml
+          if-no-files-found: error
           retention-days: 30
 
   package-e2e:
diff --git a/.gitignore b/.gitignore
index 0ff55fdcf..114a6eb6f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -34,6 +34,8 @@ codedb.snapshot
 htmlcov/
 .coverage
 coverage/
+.vitest-reports/
+test-results.xml
 .turbo/
 
 # OS
diff --git a/AGENTS.md b/AGENTS.md
index 7b0ec76d0..6a143b947 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -57,7 +57,7 @@ See [docs/architecture.mermaid](docs/architecture.mermaid) for a visual architec
 - `npm run test:fast`: run the parallel test project without the serial integration group.
 - `npm run test:integration`: run the serial filesystem, process, and CLI integration group.
 - `npm run test:watch`: watch tests affected by working-tree changes in the parallel project, without coverage.
-- `npm run test:coverage`: run the complete suite with coverage; CI owns verbose and JUnit reporting.
+- `npm run test:coverage`: run the complete suite with coverage; CI shards the suite and owns JUnit reporting.
 - `npm run typecheck`: run strict TypeScript checks without emitting files.
 - `npm run lint`: apply oxlint rules (complexity, max-lines, unused vars, and TypeScript-specific checks).
 - `npm run lint:fix`: auto-fix oxlint violations where possible.
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 8673efacb..6e92be536 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -40,14 +40,15 @@ artifact; the generated HTML is not committed.
 Local `npm test` runs without coverage, retries, or verbose output. Use `npm run
 test:fast` for the parallel group, `npm run test:integration` for serial
 filesystem/process/CLI cases, and `npm run test:watch` to watch tests affected by
-working-tree changes. CI runs `npm run test:ci`, which adds coverage, retries,
-verbose output, and JUnit results. Coverage thresholds remain in
+working-tree changes. CI splits the complete suite across two native Vitest
+shards, then merges their coverage and JUnit reports. `npm run test:ci` runs the
+equivalent unsharded gate locally. Coverage thresholds remain in
 `vitest.config.ts`.
 
 CI installs dependencies once for all static checks, cancels superseded PR
-runs, and skips package and Windows lanes when a PR changes only files outside
-the package/runtime/test boundary. TypeDoc renders only in pull-request CI; it
-does not run in local commit or pre-push hooks, or in post-merge `main` CI.
+runs, and skips package, Windows, and full test lanes for documentation-only
+pull requests. TypeDoc renders only in pull-request CI; it does not run in local
+commit or pre-push hooks, or in post-merge `main` CI.
 
 Tests that need a temporary directory must use
 `createTestTempDirectory` from `tests/fixtures/temporaryDirectory.ts`. The
diff --git a/package.json b/package.json
index ff610b2c0..5e23ef1c8 100644
--- a/package.json
+++ b/package.json
@@ -84,7 +84,10 @@
     "test:integration": "vitest run --project serial-integration",
     "pretest:coverage": "npm run build:cached",
     "test:coverage": "vitest run --coverage.enabled --coverage.provider=v8",
-    "test:ci": "npm run test:coverage -- --reporter=verbose --reporter=junit --outputFile.junit=test-results.xml",
+    "test:ci": "npm run test:coverage -- --reporter=default --reporter=junit --outputFile.junit=test-results.xml",
+    "pretest:ci:shard": "npm run build:cached",
+    "test:ci:shard": "vitest run --coverage.enabled --coverage.provider=v8 --coverage.thresholds.lines=0 --coverage.thresholds.functions=0 --coverage.thresholds.branches=0 --coverage.thresholds.statements=0 --reporter=default --reporter=blob",
+    "test:ci:merge": "vitest --merge-reports --coverage.enabled --coverage.provider=v8 --reporter=default --reporter=junit --outputFile.junit=test-results.xml",
     "pretest:verbose": "npm run build:cached",
     "test:verbose": "vitest run --reporter=verbose",
     "pretest:watch": "npm run build:cached",
diff --git a/tests/packageInstallWorkflow.test.ts b/tests/packageInstallWorkflow.test.ts
index b1ed2a5a1..9b48d3303 100644
--- a/tests/packageInstallWorkflow.test.ts
+++ b/tests/packageInstallWorkflow.test.ts
@@ -20,6 +20,18 @@ describe("package installation workflows", () => {
     expect(continuousIntegration).toContain("npm run verify:package");
     expect(continuousIntegration).toContain("name: Static checks");
     expect(continuousIntegration).toContain("npm run check:ci");
+    expect(continuousIntegration).toContain("shard: [1/2, 2/2]");
+    expect(continuousIntegration).toContain("needs: [changes, test-shard]");
+    expect(continuousIntegration).toContain("if-no-files-found: error");
+    expect(continuousIntegration).toContain("overwrite: true");
+    expect(continuousIntegration).toContain(
+      "code: ${{ steps.package.outputs.required }}",
+    );
+    expect(continuousIntegration).toContain("CODE_REQUIRED:");
+    expect(continuousIntegration).toContain(
+      'test "${CODE_REQUIRED}" != "true" || test "${SHARD_RESULT}" = "success"',
+    );
+    expect(continuousIntegration).toContain("npm run test:ci:merge");
     expect(continuousIntegration).toContain("needs: changes");
     expect(continuousIntegration).toContain(
       "cancel-in-progress: ${{ github.event_name == 'pull_request' }}",