ci: add cargo-deny supply-chain gate for Rust dependencies

.github/workflows/ci.yml

@@ -35,3 +35,14 @@ jobs:
         with:
           python-version: '3.x'
       - run: python scripts/check-secrets.py
+
+  cargo-deny:
+    name: Dependency audit
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+      # Commit-pinned (v2.0.20): a supply-chain gate must not itself depend on a
+      # mutable action tag. Config lives in deny.toml at the repo root.
+      - uses: EmbarkStudios/cargo-deny-action@bb137d7af7e4fb67e5f82a49c4fce4fad40782fe # v2.0.20
+        with:
+          command: check advisories bans sources

deny.toml

@@ -0,0 +1,31 @@
+# cargo-deny configuration — supply-chain gate for the Rust dependency tree.
+# Enforced in CI (.github/workflows/ci.yml). Docs: https://embarkstudios.github.io/cargo-deny/
+#
+# Scope is intentionally the security-relevant checks:
+#   * advisories — known vulnerabilities / RUSTSEC advisories, yanked crates
+#   * bans       — wildcard version requirements (and duplicate-version noise)
+#   * sources    — dependencies must come from the official crates.io registry
+#
+# License compliance is deliberately left out for now so this gate stays focused
+# on security and does not fail on license classification; it can be enabled as
+# a follow-up by adding a `[licenses]` allow-list and `check licenses` in CI.
+
+[advisories]
+# RUSTSEC advisory database. cargo-deny errors on vulnerabilities by default.
+# Refuse yanked crates — a yanked dependency is a supply-chain smell.
+yanked = "deny"
+# Only add advisory IDs here with a written justification, never silently.
+ignore = []
+
+[bans]
+# Duplicate transitive versions are common and noisy — surface but don't fail.
+multiple-versions = "warn"
+# Our own crates must pin real version requirements, never "*".
+wildcards = "deny"
+
+[sources]
+# Only the official crates.io registry is trusted. Reject unknown registries
+# and any git sources (there are none today).
+unknown-registry = "deny"
+unknown-git = "deny"
+allow-registry = ["https://github.com/rust-lang/crates.io-index"]