diff --git a/.github/workflows/runtime-adoption-validation.yml b/.github/workflows/runtime-adoption-validation.yml
new file mode 100644
index 0000000..e0151f8
--- /dev/null
+++ b/.github/workflows/runtime-adoption-validation.yml
@@ -0,0 +1,168 @@
+name: Runtime adoption validation
+
+on:
+  pull_request:
+    branches: [main]
+    paths:
+      - .github/workflows/runtime-adoption-validation.yml
+
+permissions:
+  contents: read
+
+env:
+  PROOFDIFF_FIX_SHA: 1f2e8b00e1c3923d4d678a933bec80ad605593ed
+
+jobs:
+  zod-vitest:
+    name: Real repo / Zod / fixed targeted Vitest
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+      - uses: actions/setup-node@v7
+        with:
+          node-version: 24
+      - uses: pnpm/action-setup@v4
+        with:
+          version: 10.12.1
+          run_install: false
+      - name: Acquire exact ProofDiff fix commit
+        shell: bash
+        run: |
+          mkdir -p work/proofdiff-fixed
+          cd work/proofdiff-fixed
+          git init -q
+          git remote add origin https://github.com/hzw0813/proofdiff.git
+          git fetch --quiet --depth=1 origin "$PROOFDIFF_FIX_SHA"
+          git checkout --quiet --detach "$PROOFDIFF_FIX_SHA"
+          test "$(git rev-parse HEAD)" = "$PROOFDIFF_FIX_SHA"
+          npm ci
+          npm run build
+      - name: Acquire pinned Zod
+        shell: bash
+        run: |
+          mkdir -p work/zod
+          cd work/zod
+          git init -q
+          git remote add origin https://github.com/colinhacks/zod.git
+          git fetch --quiet --depth=1 origin 2d90846af918af9602e088812d63a035d47cdbe4
+          git checkout --quiet --detach 2d90846af918af9602e088812d63a035d47cdbe4
+          test "$(git rev-parse HEAD)" = "2d90846af918af9602e088812d63a035d47cdbe4"
+      - name: Install pinned repository dependencies
+        working-directory: work/zod
+        run: pnpm install --frozen-lockfile --ignore-scripts
+      - name: Create syntax-preserving source mutation
+        shell: bash
+        run: |
+          printf '\n// ProofDiff runtime adoption validation: syntax-preserving no-op.\n' >> work/zod/packages/zod/src/v3/types.ts
+      - name: Require real exact-target evidence from fixed observer
+        shell: bash
+        run: |
+          node --input-type=module <<'NODE'
+          import path from 'node:path';
+          import { pathToFileURL } from 'node:url';
+
+          const proofdiffModule = pathToFileURL(path.resolve('work/proofdiff-fixed/dist/analyze.js')).href;
+          const { analyzeRepository } = await import(proofdiffModule);
+          const root = path.resolve('work/zod');
+          const changedPath = 'packages/zod/src/v3/types.ts';
+          const expectedTest = 'packages/zod/src/v3/tests/string.test.ts';
+          const targetId = 'js:test:test:targeted:vitest';
+
+          const staticReport = await analyzeRepository({ repo: root, runChecks: false });
+          const target = staticReport.discoveredChecks.find((check) => check.id === targetId);
+          if (!target) throw new Error(`Missing ${targetId}`);
+          if (!(target.targetFiles ?? []).includes(expectedTest)) {
+            throw new Error(`Expected ${expectedTest} in targeted files; got ${(target.targetFiles ?? []).join(', ')}`);
+          }
+          console.log('Fix commit:', process.env.PROOFDIFF_FIX_SHA);
+          console.log('Targeted check discovered:', target.id);
+          console.log('Target count:', target.targetFiles?.length ?? 0);
+
+          const report = await analyzeRepository({
+            repo: root,
+            runChecks: true,
+            selectedChecks: [targetId],
+            timeoutMs: 180_000,
+            maxOutputBytes: 512_000,
+          });
+          const result = report.checks.find((check) => check.id === targetId);
+          if (!result) throw new Error(`Missing executed ${targetId}`);
+          if (result.status !== 'passed') throw new Error(`Targeted check failed: ${result.status}`);
+
+          const expectedObservation = result.targetObservations?.find(
+            (item) => item.path === expectedTest || item.runnerPath === expectedTest,
+          );
+          if (!expectedObservation) throw new Error(`No exact observation for ${expectedTest}`);
+          console.log('Expected target observation:', JSON.stringify(expectedObservation));
+          if (expectedObservation.outcome !== 'passed') {
+            throw new Error(`Expected exact target to pass, got ${expectedObservation.outcome}`);
+          }
+
+          const observed = result.targetObservations?.filter((item) => item.outcome !== 'not-observed') ?? [];
+          console.log('Observed exact targets:', observed.length, '/', result.targetObservations?.length ?? 0);
+          if (observed.length === 0) throw new Error('Observer still produced no exact target observations');
+
+          const assessment = report.assessments.find((item) => item.file.path === changedPath);
+          if (!assessment) throw new Error(`Missing assessment for ${changedPath}`);
+          console.log('Changed source assessment:', assessment.status);
+          console.log('Strongest evidence:', assessment.evidenceBoundary?.strongestEvidence);
+          if (assessment.status !== 'verified') {
+            throw new Error(`Expected source to be verified, got ${assessment.status}`);
+          }
+          if (assessment.evidenceBoundary?.strongestEvidence !== 'related-test-file-passed') {
+            throw new Error(`Unexpected strongest evidence: ${assessment.evidenceBoundary?.strongestEvidence}`);
+          }
+          NODE
+
+  vitest-monorepo-negative:
+    name: Real repo / Vitest monorepo / orchestration stays opaque
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+      - uses: actions/setup-node@v7
+        with:
+          node-version: 24
+      - name: Acquire exact ProofDiff fix commit
+        shell: bash
+        run: |
+          mkdir -p work/proofdiff-fixed
+          cd work/proofdiff-fixed
+          git init -q
+          git remote add origin https://github.com/hzw0813/proofdiff.git
+          git fetch --quiet --depth=1 origin "$PROOFDIFF_FIX_SHA"
+          git checkout --quiet --detach "$PROOFDIFF_FIX_SHA"
+          test "$(git rev-parse HEAD)" = "$PROOFDIFF_FIX_SHA"
+          npm ci
+          npm run build
+      - name: Acquire pinned Vitest monorepo without installing dependencies
+        shell: bash
+        run: |
+          mkdir -p work/vitest
+          cd work/vitest
+          git init -q
+          git remote add origin https://github.com/vitest-dev/vitest.git
+          git fetch --quiet --depth=1 --filter=blob:none origin 667c13954daff2d1bec8a866702da8934b9ce539
+          git checkout --quiet --detach 667c13954daff2d1bec8a866702da8934b9ce539
+          test "$(git rev-parse HEAD)" = "667c13954daff2d1bec8a866702da8934b9ce539"
+          printf '\n// ProofDiff runtime adoption validation: syntax-preserving no-op.\n' >> packages/utils/src/error.ts
+      - name: Require root workspace orchestration to remain opaque
+        shell: bash
+        run: |
+          node --input-type=module <<'NODE'
+          import path from 'node:path';
+          import { pathToFileURL } from 'node:url';
+
+          const proofdiffModule = pathToFileURL(path.resolve('work/proofdiff-fixed/dist/analyze.js')).href;
+          const { analyzeRepository } = await import(proofdiffModule);
+          const root = path.resolve('work/vitest');
+          const report = await analyzeRepository({ repo: root, runChecks: false });
+          const rootTest = report.discoveredChecks.find((check) => check.id === 'js:test:test');
+          if (!rootTest) throw new Error('Expected root test check discovery');
+          const invented = report.discoveredChecks.filter((check) => check.id.startsWith('js:test:test:targeted:'));
+          console.log('Fix commit:', process.env.PROOFDIFF_FIX_SHA);
+          console.log('Root test command:', rootTest.command, ...(rootTest.args ?? []));
+          console.log('Invented exact-target checks:', invented.length);
+          if (invented.length !== 0) {
+            throw new Error(`Workspace orchestration unexpectedly became exact-target evidence: ${invented.map((item) => item.id).join(', ')}`);
+          }
+          NODE