ci: add a cargo-audit dependency vulnerability gate

Runs actions-rust-lang/audit after the offline tests in the test job: a
crate in Cargo.lock with an unfixed security advisory fails the build.
Verified locally against the current lockfile (0 vulnerabilities; the 3
warnings — unmaintained dotenv/proc-macro-error2 and transitive anyhow
unsoundness — do not fail by default).

.github/workflows/ci.yml

@@ -4,8 +4,9 @@ name: CI
 # job that exercises the real source sites and the token-gated pixiv tests.
 #
 # Layering:
-#   test  — fmt + clippy + the full offline unit suite. Runs on every push
-#           and PR, including forks (it needs no secrets).
+#   test  — fmt + clippy + the full offline unit suite + cargo-audit
+#           dependency gate. Runs on every push and PR, including forks
+#           (it needs no secrets).
 #   live  — the #[ignore]d live-network tests plus the pixiv tests that are
 #           gated on PIXIV_REFRESH_TOKEN. Runs on schedule / manual dispatch
 #           / tag pushes only, because pull requests from forks cannot read
@@ -42,6 +43,12 @@ jobs:
         run: cargo clippy --workspace --all-targets -- -D warnings
       - name: Run offline tests
         run: cargo test --workspace
+      # Dependency vulnerability gate: fails the build when a crate in
+      # Cargo.lock has an unfixed security advisory. Unmaintained/unsound
+      # *warnings* (dotenv, proc-macro-error2, anyhow transitive) do not fail
+      # the build by default; the advisory DB is cached across runs.
+      - name: Audit dependencies
+        uses: actions-rust-lang/audit@v1
 
   live:
     needs: test

AGENTS.md

@@ -100,6 +100,6 @@ Docker: `docker build -t tgxmb .` then `docker run --rm -d --name tgxmb --env-fi
 - No mocking framework anywhere (no mockito/wiremock/mockall). Conventions: pure-function units (regex parsing, serde round-trips, chunking, retry math) tested synchronously; async tests use real dependencies — file-backed SQLite via `tempfile` (`queue.rs::new_queue()` helper), live network fetches.
 - Live-network tests exist in `site/twitter/interface.rs` (5), `site/bsky/interface.rs` (2), `site/pixiv/api.rs` (1); `photo.rs` adds one `#[ignore = "heavy: …"]` test. Test gating convention (enforced by `.github/workflows/ci.yml`): pure unit tests always run; live-network tests carry `#[ignore = "live network: ..."]` (run via `cargo test --workspace -- --ignored live`); token-gated pixiv tests early-return when `PIXIV_REFRESH_TOKEN` is absent **or empty** (an unset GitHub secret arrives as `""` — `is_err()` alone would run them tokenless and fail). Run the full offline suite with `cargo test --workspace`.
 - Fixtures are inline `serde_json::json!` builder fns (`fixture()`, `thread_json()`, `illust_json()`), not files. The shared `CLIENT` sets `pool_max_idle_per_host(0)` under `#[cfg(test)]` to avoid cross-runtime `DispatchGone`.
-- **CI** — `.github/workflows/ci.yml` runs `cargo fmt --check` + `cargo clippy --workspace --all-targets -- -D warnings` + `cargo test --workspace` (offline, no secrets, on every push/PR) and a `live` job (schedule/manual/tag only, `PIXIV_REFRESH_TOKEN`/`TWITTER_AUTH_TOKEN` from secrets, `continue-on-error`) for the `#[ignore]`d live + token tests. `.github/workflows/docker.yml` builds/pushes the image only.
+- **CI** — `.github/workflows/ci.yml` runs `cargo fmt --check` + `cargo clippy --workspace --all-targets -- -D warnings` + `cargo test --workspace` + a `actions-rust-lang/audit` dependency-vulnerability gate (offline, no secrets, on every push/PR) and a `live` job (schedule/manual/tag only, `PIXIV_REFRESH_TOKEN`/`TWITTER_AUTH_TOKEN` from secrets, `continue-on-error`) for the `#[ignore]`d live + token tests. `.github/workflows/docker.yml` builds/pushes the image only.
 - Untested and hard to test without a mock seam: `handlers.rs` (depends directly on teloxide `Bot`); `main.rs`, `config.rs`, `state.rs`; `media.rs`, `lib.rs`, all `model.rs`.
 - No coverage tracking.