diff --git a/backend/app/app_compile_contract.py b/backend/app/app_compile_contract.py
index bac1408ca..f42a38bd3 100644
--- a/backend/app/app_compile_contract.py
+++ b/backend/app/app_compile_contract.py
@@ -101,10 +101,17 @@ def runtime_library_aliases() -> tuple[tuple[str, Path], ...]:
   ``app_runtime_inject.js``. React then sees two dispatchers and every hook
   fails at first render. Package-root aliases apply to the root and its subpaths
   (for example ``react/jsx-runtime``), keeping each supported library singular.
+
+  Three's documented ``three/addons/*`` export is backed by the physical
+  ``examples/jsm`` directory rather than an ``addons`` directory. Once the
+  package root is replaced with an absolute alias, esbuild no longer consults
+  Three's package exports for that subpath. Pin the public addons spelling to
+  its runtime-owned physical directory before adding the package roots.
   """
   node_path = runtime_node_path()
   roots = sorted({_package_root(specifier) for specifier in BUNDLED_RUNTIME_LIBS})
-  return tuple((root, node_path / root) for root in roots)
+  subpaths = (("three/addons", node_path / "three" / "examples" / "jsm"),)
+  return subpaths + tuple((root, node_path / root) for root in roots)
 
 
 NO_DEFAULT_EXPORT_ERROR = (
diff --git a/backend/tests/test_runtime_libs.py b/backend/tests/test_runtime_libs.py
index 17690a054..cbda06c26 100644
--- a/backend/tests/test_runtime_libs.py
+++ b/backend/tests/test_runtime_libs.py
@@ -21,6 +21,7 @@
   mobius_runtime_path,
   runtime_library_aliases,
   runtime_inject_path,
+  runtime_node_path,
 )
 
 
@@ -121,6 +122,50 @@ def test_app_local_or_transitive_react_cannot_shadow_platform_runtime(tmp_path):
   assert "shadow-react-copy" not in output.read_text()
 
 
+def test_three_addons_resolve_from_the_pinned_runtime(tmp_path):
+  """Documented addons imports must survive package-root runtime pinning."""
+  aliases = dict(runtime_library_aliases())
+  assert aliases["three"] == runtime_node_path() / "three"
+  assert (
+    aliases["three/addons"]
+    == runtime_node_path() / "three" / "examples" / "jsm"
+  )
+
+  entry = tmp_path / "three-addons.jsx"
+  output = tmp_path / "three-addons.js"
+  metafile = tmp_path / "three-addons-meta.json"
+  entry.write_text(
+    """import { OrbitControls } from 'three/addons/controls/OrbitControls.js'
+import { STLLoader } from 'three/addons/loaders/STLLoader.js'
+
+export default function ThreeAddonsFixture() {
+  return [OrbitControls.name, STLLoader.name]
+}
+"""
+  )
+
+  completed = subprocess.run(
+    esbuild_command(entry, output, metafile=metafile),
+    capture_output=True,
+    check=False,
+    env=esbuild_environment(),
+    text=True,
+    timeout=ESBUILD_TIMEOUT_SECS,
+  )
+  assert completed.returncode == 0, completed.stderr
+
+  metadata = json.loads(metafile.read_text())
+  entry_outputs = [
+    details for details in metadata["outputs"].values()
+    if details.get("entryPoint")
+  ]
+  assert len(entry_outputs) == 1
+  assert entry_outputs[0].get("imports") == [], (
+    "Three addons escaped the pinned self-contained app bundle"
+  )
+  assert output.is_file() and output.stat().st_size > 0
+
+
 def test_app_hosts_have_no_runtime_import_map_or_static_module_imports():
   frame = FRAME.read_text()
   standalone = STANDALONE.read_text()