test: add characterization tests for core modules

33 tests covering env/io helpers, config parsers, pipeline meta I/O,
worker inbox logic, and FastAPI smoke routes. No gmic/rembg subprocesses.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/test_env_utils.py

@@ -0,0 +1,22 @@
+"""Tests for env_utils."""
+
+from __future__ import annotations
+
+from app.env_utils import env_bool
+
+
+def test_env_bool_default(monkeypatch) -> None:
+    monkeypatch.delenv("TEST_FLAG", raising=False)
+    assert env_bool("TEST_FLAG", True) is True
+    assert env_bool("TEST_FLAG", False) is False
+
+
+def test_env_bool_truthy(monkeypatch) -> None:
+    for value in ("1", "true", "TRUE", "yes", "on"):
+        monkeypatch.setenv("TEST_FLAG", value)
+        assert env_bool("TEST_FLAG", False) is True
+
+
+def test_env_bool_falsy(monkeypatch) -> None:
+    monkeypatch.setenv("TEST_FLAG", "0")
+    assert env_bool("TEST_FLAG", True) is False