feat(zygote): Django test database initialization before fork

src/execution/scheduler.rs

@@ -123,6 +123,10 @@ pub struct Scheduler {
     hook_registry: HookRegistry,
     /// Project root directory for resolving hook paths
     project_root: PathBuf,
+    /// Reuse existing test database (--reuse-db)
+    reuse_db: bool,
+    /// Force recreation of test database (--create-db)
+    create_db: bool,
 }
 
 impl Scheduler {
@@ -143,6 +147,8 @@ impl Scheduler {
             None,
             hook_registry,
             project_root,
+            false,
+            false,
         )
     }
 
@@ -165,6 +171,8 @@ impl Scheduler {
             None,
             hook_registry,
             project_root,
+            false,
+            false,
         )
     }
 
@@ -179,6 +187,8 @@ impl Scheduler {
         timeout_hook: Option<String>,
         hook_registry: HookRegistry,
         project_root: PathBuf,
+        reuse_db: bool,
+        create_db: bool,
     ) -> Result<Self> {
         let max_workers = log_capture.slot_count();
 
@@ -202,6 +212,8 @@ impl Scheduler {
             timeout_hook,
             hook_registry,
             project_root,
+            reuse_db,
+            create_db,
         })
     }
 
@@ -518,8 +530,8 @@ impl Scheduler {
             cached_effects,
             markers: test.markers.clone(),
             marker_info: test.marker_info.clone(),
-            reuse_db: false,
-            create_db: false,
+            reuse_db: self.reuse_db,
+            create_db: self.create_db,
         };
 
         // Use encode_with_length which includes protocol header

src/execution/zygote.rs

@@ -661,7 +661,10 @@ pub fn entrypoint(cmd_socket: UnixStream, result_socket: UnixStream) -> Result<(
         }
 
         // Django Detection & Setup (Batteries-Included)
-        // Initialize Django in Zygote so workers inherit the pre-warmed state
+        // Initialize Django in Zygote so workers inherit the pre-warmed state.
+        // NOTE: We do NOT warm up DB connections here. setup_databases() creates
+        // a test DB after init_session(), and connections are closed before fork
+        // so workers get fresh file descriptors.
         py.run(
             c_str!(r#"
 import os
@@ -670,20 +673,9 @@ import sys
 try:
     import django
 
-    # Check if DJANGO_SETTINGS_MODULE is already set
     if 'DJANGO_SETTINGS_MODULE' in os.environ:
         django.setup()
         print(f'[tach:zygote] Django initialized: {os.environ["DJANGO_SETTINGS_MODULE"]}', file=sys.stderr)
-
-        # CRITICAL: Warm up DB connections before forking
-        # File descriptors must exist in Zygote to be inherited by workers
-        try:
-            from django.db import connections
-            for alias in connections:
-                connections[alias].ensure_connection()
-            print(f'[tach:zygote] Django DB connections warmed up', file=sys.stderr)
-        except Exception as e:
-            print(f'[tach:zygote] Django DB warmup failed: {e}', file=sys.stderr)
 except ImportError:
     pass  # Django not installed, skip
 except Exception as e:
@@ -708,6 +700,24 @@ except Exception as e:
         let target_path = std::env::var("TACH_TARGET_PATH").unwrap_or_else(|_| cwd_str.clone());
         harness.getattr("init_session")?.call1((&target_path,))?;
 
+        // Django Test Database: Create test DB after pytest is configured but
+        // before workers fork. Reads TACH_REUSE_DB/TACH_CREATE_DB env vars.
+        // Connections are closed before fork so workers get fresh FDs.
+        py.run(
+            c_str!(
+                r#"
+try:
+    import tach_harness
+    tach_harness._setup_django_test_db()
+except Exception as e:
+    import sys
+    print(f'[tach:zygote] Django test DB setup error: {e}', file=sys.stderr)
+"#
+            ),
+            None,
+            None,
+        )?;
+
         // HOOK EFFECT BRIDGE (v0.2.0): Retrieve session effects from Python
         // After init_session(), Python has recorded effects in _SESSION_HOOK_EFFECTS.
         // We retrieve them here and will send them to the Supervisor for HookRegistry population.

src/main.rs

@@ -201,6 +201,15 @@ fn main() -> Result<()> {
     // SAFETY: Same as above - called before worker threads spawn.
     unsafe { std::env::set_var("TACH_TARGET_PATH", &cli.path) };
 
+    // Set Django test DB flags for Zygote to read during setup_databases()
+    // SAFETY: Same as above - called before worker threads spawn.
+    if cli.reuse_db {
+        unsafe { std::env::set_var("TACH_REUSE_DB", "1") };
+    }
+    if cli.create_db {
+        unsafe { std::env::set_var("TACH_CREATE_DB", "1") };
+    }
+
     // --- LIFECYCLE SETUP ---
     debugger::install_panic_hook();
 
@@ -1160,6 +1169,8 @@ fn run_tests(
                 timeout_hook,
                 hook_registry,
                 project_root,
+                std::env::var("TACH_REUSE_DB").unwrap_or_default() == "1",
+                std::env::var("TACH_CREATE_DB").unwrap_or_default() == "1",
             )?;
 
             let stats = scheduler.run(runnable_tests, reporter)?;