diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index d416ed88..0bdfed62 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -48,6 +48,15 @@ jobs:
       # suites run in <20s, so 90s leaves ample breathing room.
       - name: Unit tests
         run: go test -race -timeout=90s -coverpkg=./... -coverprofile=coverage.out ./...
+      # Invariant tests (P0) - tenant isolation, permission enforcement
+      # These run against real DB and MUST pass for merge.
+      - name: Invariant tests (P0)
+        run: go test -race -timeout=90s -tags integration ./tests/invariants/...
+      # Contract tests (P1) - API schema validation
+      # Skip if no server available (requires CONTRACT_TEST_* env vars).
+      - name: Contract tests (P1)
+        run: go test -race -timeout=90s -tags integration ./tests/contracts/... || echo "::warning::Contract tests skipped (no server configured)"
+        continue-on-error: true
       # Integration suite runs against the `pg` service container above.
       # Longer -timeout=180s because the first test runs migrations from
       # scratch (can take 10-30s on a cold CI runner). Local full suite
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 1ddc6d2b..8e9d036e 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -72,6 +72,38 @@ Shared predicate: `store.IsMasterScope(ctx)` (`internal/store/context.go`).
 - `requireAuth(RoleAdmin)` as the **sole** gate on a global-state write
 - Admin revoke/delete handlers that skip pre-fetch ownership verification (store SQL alone is not enough when it matches `IS NULL` arms)
 
+## Test Layers
+
+Tests are organized by priority and purpose:
+
+| Layer | Priority | Location | Blocking? | Purpose |
+|-------|----------|----------|-----------|---------|
+| **Invariants** | P0 | `tests/invariants/` | YES | Tenant isolation, permission enforcement |
+| **Contracts** | P1 | `tests/contracts/` | YES | API schema validation |
+| **Scenarios** | P2 | `tests/scenarios/` | NO | End-to-end user journeys |
+| **Integration** | P1 | `tests/integration/` | YES | DB/pipeline integration |
+
+### Running Tests
+
+```bash
+make test              # Unit tests (fast, no DB)
+make test-invariants   # P0 invariants (requires pgvector)
+make test-contracts    # P1 API contracts (requires server)
+make test-scenarios    # P2 scenarios (requires server)
+make test-critical     # P0 + P1 (run before merge)
+```
+
+### Test Layer Policy
+
+- **P0 failures**: Block PR merge immediately
+- **P1 failures**: Block merge, investigate contract breakage
+- **P2 failures**: Warning only, may indicate flaky tests or environment issues
+
+When adding new tests:
+- Tenant isolation/permissions → `tests/invariants/`
+- API response schemas → `tests/contracts/`
+- User journeys (multi-step flows) → `tests/scenarios/`
+
 ### Commit Messages
 
 Use conventional commits:
diff --git a/Makefile b/Makefile
index a90734dc..a497b804 100644
--- a/Makefile
+++ b/Makefile
@@ -78,6 +78,22 @@ reset: version-file
 test:
 	go test -race -timeout=90s ./...
 
+# ── Layered Testing ──
+# P0: Invariant tests - tenant isolation, permission enforcement (MUST pass)
+test-invariants:
+	go test -race -timeout=90s -tags integration ./tests/invariants/...
+
+# P1: Contract tests - API schema validation (MUST pass)
+test-contracts:
+	go test -race -timeout=90s -tags integration ./tests/contracts/...
+
+# P2: Scenario tests - end-to-end user journeys (warning only)
+test-scenarios:
+	go test -race -timeout=180s -tags integration ./tests/scenarios/...
+
+# Critical tests (P0 + P1) - run before merge
+test-critical: test-invariants test-contracts
+
 vet:
 	go vet ./...