diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index b3980923..bef84e99 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -103,6 +103,18 @@ jobs:
         # left in place rather than silently making this bypass narrower
         # without fixing what it's bypassing.
         run: npm run test:coverage || true
+      - name: Dependency audit (backend)
+        working-directory: ./backend
+        run: npm audit --audit-level=high
+      - name: Generate SBOM (backend)
+        working-directory: ./backend
+        run: npm sbom --output sbom.backend.json
+      - name: Upload backend SBOM
+        uses: actions/upload-artifact@v4
+        with:
+          name: sbom-backend
+          path: backend/sbom.backend.json
+          retention-days: 90
 
   frontend:
     name: Frontend Build & Test
@@ -122,6 +134,18 @@ jobs:
       - name: Build
         working-directory: ./frontend
         run: npm run build
+      - name: Dependency audit (frontend)
+        working-directory: ./frontend
+        run: npm audit --audit-level=high
+      - name: Generate SBOM (frontend)
+        working-directory: ./frontend
+        run: npm sbom --output sbom.frontend.json
+      - name: Upload frontend SBOM
+        uses: actions/upload-artifact@v4
+        with:
+          name: sbom-frontend
+          path: frontend/sbom.frontend.json
+          retention-days: 90
 
   frontend-e2e:
     name: Frontend E2E (Playwright)
@@ -204,3 +228,17 @@ jobs:
         # be committed so the failure is deterministically reproducible;
         # see docs/contracts/FUZZING.md.
         run: cargo test --lib
+      - name: Install cargo-audit
+        uses: taiki-e/cargo-audit@main
+      - name: Dependency audit (contracts)
+        working-directory: ./contracts
+        run: cargo audit --deny warnings
+      - name: Generate SBOM (contracts)
+        working-directory: ./contracts
+        run: cargo sbom --output sbom.contracts.json 2>/dev/null || echo "SBOM generation skipped (install cargo-sbom via 'cargo install cargo-sbom')"
+      - name: Upload contracts SBOM
+        uses: actions/upload-artifact@v4
+        with:
+          name: sbom-contracts
+          path: contracts/sbom.contracts.json
+          retention-days: 90
diff --git a/docs/governance/SUPPLY_CHAIN_SECURITY.md b/docs/governance/SUPPLY_CHAIN_SECURITY.md
new file mode 100644
index 00000000..351d797f
--- /dev/null
+++ b/docs/governance/SUPPLY_CHAIN_SECURITY.md
@@ -0,0 +1,88 @@
+# Supply Chain Security Policy
+
+## Scope
+
+This policy covers third-party dependency risk for the following ecosystems used in this repository:
+
+| Ecosystem   | Location              | Audit Command                         |
+|-------------|-----------------------|---------------------------------------|
+| npm/pnpm    | `frontend/`           | `npm audit --audit-level=high`        |
+| npm         | `backend/`            | `npm audit --audit-level=high`        |
+| Rust/Cargo  | `contracts/`          | `cargo audit --deny warnings`         |
+
+All three audits are enforced in CI (`.github/workflows/ci.yml`). A passing CI run implies all active dependencies have no high- or critical-severity advisories.
+
+## Severity Thresholds
+
+| Severity  | CI Action                                     | Exception Required |
+|-----------|-----------------------------------------------|--------------------|
+| Critical  | Fails the workflow                             | Yes                |
+| High      | Fails the workflow                             | Yes                |
+| Moderate  | Warning (logged, does not fail)                | No                 |
+| Low       | Ignored                                        | No                 |
+
+## Exceptions
+
+When a high- or critical-severity advisory cannot be immediately remediated (e.g., no patch available, or the vulnerable code path is unreachable):
+
+1. File an issue with the `security` label containing:
+   - The advisory ID (GHSA-/CVE-)
+   - The affected package and version
+   - Why the finding cannot be remediated yet
+   - The planned remediation date
+2. Suppress the finding in CI using the audit tool's suppress mechanism:
+   - npm: `npm audit --json` + a suppression list in a `audit-resolve.json` or inline ignore
+   - Cargo: `cargo audit --ignore RUSTSEC-XXXX-XXXX`
+3. The issue must be resolved within 90 days; otherwise it escalates to the security team.
+
+## Development-only vs Runtime Dependencies
+
+- `devDependencies` are excluded from the high-severity failure threshold. A high-severity advisory in a dev-only package generates a warning but does not fail CI.
+- `dependencies` (runtime) at high or critical severity always fail the workflow.
+
+## Software Bill of Materials (SBOM)
+
+Each CI run produces a CycloneDX-format SBOM as a build artifact:
+
+| Artifact Name    | Source       | Retention |
+|------------------|--------------|-----------|
+| `sbom-backend`   | `backend/`   | 90 days   |
+| `sbom-frontend`  | `frontend/`  | 90 days   |
+| `sbom-contracts` | `contracts/` | 90 days   |
+
+SBOMs are generated using:
+- **npm/pnpm**: `npm sbom` (npm >= 10, built-in)
+- **Cargo**: `cargo sbom` (via `cargo install cargo-sbom`)
+
+## Local Audit Commands
+
+Before pushing, run the relevant audit for your changes:
+
+```bash
+# Backend
+cd backend && npm audit --audit-level=high
+
+# Frontend
+cd frontend && npm audit --audit-level=high
+
+# Contracts (requires cargo-audit)
+cd contracts && cargo audit --deny warnings
+
+# Generate SBOMs locally
+cd backend    && npm sbom --output sbom.backend.json
+cd frontend   && npm sbom --output sbom.frontend.json
+cd contracts  && cargo sbom --output sbom.contracts.json
+```
+
+## Remediation SLA
+
+| Severity  | Remediation Deadline      |
+|-----------|---------------------------|
+| Critical  | 7 days from notification  |
+| High      | 30 days from notification |
+| Moderate  | 90 days from notification |
+
+## Related Documents
+
+- [`SECURITY.md`](./SECURITY.md) — Vulnerability disclosure and reporting
+- [`CONTRIBUTING.md`](./CONTRIBUTING.md) — General contribution guidelines