fix(fuzz): repair API drift, make fuzz hermetic, add GHA smoke test

.github/workflows/fuzz.yml

@@ -0,0 +1,28 @@
+name: "Fuzz"
+
+on:
+  pull_request:
+    branches: [main]
+
+jobs:
+  fuzz:
+    name: Fuzz smoke test (10s/target)
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+    steps:
+      - name: Install Nix
+        uses: DeterminateSystems/nix-installer-action@v16
+      - name: Run the Magic Nix Cache
+        uses: DeterminateSystems/magic-nix-cache-action@v8
+      - uses: actions/checkout@v4
+      - name: Cache fuzz build artifacts
+        uses: actions/cache@v4
+        with:
+          path: fuzz/target
+          key: fuzz-${{ runner.os }}-${{ hashFiles('fuzz/Cargo.lock', 'rust-toolchain.toml') }}
+          restore-keys: |
+            fuzz-${{ runner.os }}-
+      - name: Run fuzz targets
+        env:
+          FUZZ_SECONDS: 10
+        run: nix run .#fuzz

Makefile

@@ -42,4 +42,4 @@ sqlx-prepare:
 # `nix run .#fuzz` and the Concourse `fuzz` job. Auto-discovers targets via
 # `cargo fuzz list`; runs them for $(FUZZ_TIME)s. Corpus in fuzz/corpus/ (gitignored).
 fuzz:
-	FUZZ_SECONDS=$(FUZZ_TIME) bash ci/vendor/tasks/fuzz.sh
+	SQLX_OFFLINE=true FUZZ_SECONDS=$(FUZZ_TIME) bash ci/vendor/tasks/fuzz.sh

flake.nix

@@ -375,6 +375,7 @@
       # — no Postgres. FUZZ_SECONDS etc. are passed through the environment.
       fuzz-runner = pkgs.writeShellScriptBin "fuzz" ''
         set -e
+        export SQLX_OFFLINE=true
         export PATH="${pkgs.lib.makeBinPath [
           rustToolchain
           pkgs.cargo-fuzz

fuzz/fuzz_targets/fuzz_decode_persistent_event.rs

@@ -28,7 +28,7 @@ use libfuzzer_sys::fuzz_target;
 
 use chrono::Utc;
 use obix::out::OutboxEventId;
-use obix::{EventSequence, UndecodableEventError, decode_persistent_event};
+use obix::{CommitGroupId, EventSequence, UndecodableEventError, decode_persistent_event};
 use serde::{Deserialize, Serialize};
 use uuid::Uuid;
 
@@ -58,13 +58,15 @@ fuzz_target!(|data: &[u8]| {
     let id = OutboxEventId::from(Uuid::nil());
     let sequence = 0u64;
     let recorded_at = Utc::now();
+    let commit_group = CommitGroupId::from(0i64);
 
     match decode_persistent_event::<FuzzPayload>(
         id,
         sequence,
         recorded_at,
         None,
         payload.clone(),
+        commit_group,
     ) {
         Ok(event) => {
             if must_be_ok_with_none {
@@ -86,13 +88,15 @@ fuzz_target!(|data: &[u8]| {
             assert_eq!(event.id, id);
             assert_eq!(u64::from(event.sequence), sequence);
             assert_eq!(event.recorded_at, recorded_at);
+            assert_eq!(event.commit_group, commit_group);
             assert!(event.tracing_context.is_none());
         }
         Err(UndecodableEventError {
             id: err_id,
             sequence: err_seq,
             recorded_at: err_ts,
             failure,
+            commit_group: err_cg,
         }) => {
             // `None` can never be undecodable — that's the placeholder path.
             let raw = payload
@@ -107,6 +111,7 @@ fuzz_target!(|data: &[u8]| {
             assert_eq!(err_id, id);
             assert_eq!(err_seq, EventSequence::from(sequence));
             assert_eq!(err_ts, recorded_at);
+            assert_eq!(err_cg, commit_group);
         }
     }
 });