Add custom sandbox env vars and Makefile

SANDBOX_EXTRA_ENV accepts a JSON string of extra env vars
merged into every sandbox. Makefile adds deploy/serve/test/lint/logs
targets for local development.

Author: manascb1344

Makefile

@@ -0,0 +1,16 @@
+.PHONY: deploy serve test lint logs
+
+deploy:
+	modal deploy app.py
+
+serve:
+	modal serve app.py
+
+test:
+	pytest tests/ -v
+
+lint:
+	ruff check app.py
+
+logs:
+	modal app logs modal-github-runner

app.py

@@ -109,6 +109,18 @@ def format(self, record: logging.LogRecord) -> str:
 
 MODAL_REGION = os.environ.get("MODAL_REGION", "") or None
 
+SANDBOX_EXTRA_ENV: dict = {}
+_extra_env_raw = os.environ.get("SANDBOX_EXTRA_ENV", "")
+if _extra_env_raw:
+    try:
+        parsed = json.loads(_extra_env_raw)
+        if isinstance(parsed, dict):
+            SANDBOX_EXTRA_ENV = {str(k): str(v) for k, v in parsed.items()}
+        else:
+            logger.warning("SANDBOX_EXTRA_ENV is not a JSON object, ignoring")
+    except json.JSONDecodeError:
+        logger.warning("SANDBOX_EXTRA_ENV is not valid JSON, ignoring")
+
 
 def _get_gpu_config(gpu_key: str):
     attr_name = GPU_LABEL_TO_ATTR.get(gpu_key)
@@ -720,7 +732,7 @@ async def github_webhook(request: Request):
             image=runner_image,
             app=app,
             timeout=TIMEOUT_SECONDS,
-            env={"GHA_JIT_CONFIG": jit_config},
+            env={"GHA_JIT_CONFIG": jit_config, **SANDBOX_EXTRA_ENV},
             gpu=gpu_config,
             cidr_allowlist=ALLOWED_CIDRS,
             block_network=BLOCK_NETWORK,