Gate jsbsim behind sys_platform marker for Pyodide compatibility

pyproject.toml

@@ -29,7 +29,11 @@ dependencies = [
     "pathsim",
     "numpy>=1.15",
     "scipy>=1.2",
-    "jsbsim>=1.2.4"
+    # JSBSim ships native code that can't be installed in Pyodide. The
+    # marker resolves to a normal eager install on every real platform and
+    # is skipped on Emscripten so the pure-Python parts of the toolbox
+    # (`pathsim_flight.atmosphere`, `.utils`) still install in the browser.
+    "jsbsim>=1.2.4; sys_platform != 'emscripten'",
 ]
 
 [project.optional-dependencies]

src/pathsim_flight/__init__.py

@@ -12,7 +12,14 @@
 
 __all__ = ["__version__"]
 
-# For direct block import from main package
-from .atmosphere import *
-from .jsbsim import *
-from .utils import *
+# Pure-Python submodules — eager.
+from .atmosphere import *  # noqa: F401,F403
+from .utils import *  # noqa: F401,F403
+
+# `jsbsim` wraps the native JSBSim Python bindings, which can't load in
+# Pyodide. Re-export the wrapper only when the import succeeds; on a normal
+# pip install it loads eagerly.
+try:
+    from .jsbsim import *  # noqa: F401,F403
+except ImportError:
+    pass