fix(discovery): TransactionTestCase isolation via toxic queue routing

src/discovery/resolver.rs

@@ -93,6 +93,22 @@ pub struct RunnableTest {
     pub marker_info: Vec<crate::discovery::MarkerInfo>,
 }
 
+impl RunnableTest {
+    /// Returns true if this test has `@pytest.mark.django_db(transaction=True)`.
+    ///
+    /// Transaction tests commit directly to the database, requiring process-level
+    /// isolation (toxic mode) instead of savepoint-based rollback.
+    pub fn has_django_transaction_marker(&self) -> bool {
+        self.marker_info.iter().any(|m| {
+            m.name == "django_db"
+                && m.args
+                    .get("transaction")
+                    .and_then(|v| v.as_bool())
+                    .unwrap_or(false)
+        })
+    }
+}
+
 /// A resolved fixture with full context
 #[derive(Debug, Clone)]
 pub struct ResolvedFixture {
@@ -450,7 +466,7 @@ impl<'a> Resolver<'a> {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::discovery::TestModule;
+    use crate::discovery::{MarkerInfo, TestModule};
 
     /// Helper to create a fixture definition
     fn make_fixture(name: &str, deps: Vec<&str>) -> FixtureDefinition {
@@ -875,4 +891,63 @@ mod tests {
         // Inner fixture has function scope (default)
         assert_eq!(runnable[0].fixtures[0].scope, FixtureScope::Function);
     }
+
+    #[test]
+    fn test_has_django_transaction_marker_true() {
+        let test = RunnableTest {
+            file_path: PathBuf::from("test_views.py"),
+            test_name: "test_create_user".to_string(),
+            is_async: false,
+            fixtures: vec![],
+            is_toxic: false,
+            timeout_secs: None,
+            markers: vec!["django_db".to_string()],
+            marker_info: vec![MarkerInfo {
+                name: "django_db".to_string(),
+                args: {
+                    let mut m = std::collections::HashMap::new();
+                    m.insert("transaction".to_string(), serde_json::Value::Bool(true));
+                    m
+                },
+            }],
+        };
+        assert!(test.has_django_transaction_marker());
+    }
+
+    #[test]
+    fn test_has_django_transaction_marker_false_when_no_marker() {
+        let test = RunnableTest {
+            file_path: PathBuf::from("test_utils.py"),
+            test_name: "test_parse".to_string(),
+            is_async: false,
+            fixtures: vec![],
+            is_toxic: false,
+            timeout_secs: None,
+            markers: vec![],
+            marker_info: vec![],
+        };
+        assert!(!test.has_django_transaction_marker());
+    }
+
+    #[test]
+    fn test_has_django_transaction_marker_false_when_transaction_false() {
+        let test = RunnableTest {
+            file_path: PathBuf::from("test_views.py"),
+            test_name: "test_read_user".to_string(),
+            is_async: false,
+            fixtures: vec![],
+            is_toxic: false,
+            timeout_secs: None,
+            markers: vec!["django_db".to_string()],
+            marker_info: vec![MarkerInfo {
+                name: "django_db".to_string(),
+                args: {
+                    let mut m = std::collections::HashMap::new();
+                    m.insert("transaction".to_string(), serde_json::Value::Bool(false));
+                    m
+                },
+            }],
+        };
+        assert!(!test.has_django_transaction_marker());
+    }
 }

src/main.rs

@@ -470,7 +470,8 @@ fn execute_session(
     let mut runnable_tests = runnable_tests;
     let mut toxic_test_count = 0;
     for test in &mut runnable_tests {
-        test.is_toxic = toxicity_graph.is_toxic(&test.file_path);
+        test.is_toxic =
+            toxicity_graph.is_toxic(&test.file_path) || test.has_django_transaction_marker();
         if test.is_toxic {
             toxic_test_count += 1;
         }
@@ -822,7 +823,8 @@ fn handle_dry_run_command(
     // --- TOXICITY TAGGING ---
     let mut runnable_tests = runnable_tests;
     for test in &mut runnable_tests {
-        test.is_toxic = toxicity_graph.is_toxic(&test.file_path);
+        test.is_toxic =
+            toxicity_graph.is_toxic(&test.file_path) || test.has_django_transaction_marker();
     }
 
     // --- PATH FILTERING ---

src/tach_harness.py

@@ -2784,8 +2784,13 @@ def _apply_django_db_isolation(
             "databases": None,
         }
 
-    # If transaction=True, skip isolation (test manages its own transactions)
+    # If transaction=True, the test manages its own transactions and may
+    # commit directly to the database. Savepoint-based isolation won't work
+    # because commits escape the savepoint. Instead, these tests are marked
+    # toxic so the worker exits after running — the Zygote's clean DB
+    # snapshot is restored on the next fork.
     if marker_args.get("transaction", False):
+        _close_django_connections()
         return []
 
     # Determine which databases to isolate