diff --git a/scripts/pathview_install.py b/scripts/pathview_install.py
new file mode 100644
index 00000000..7c28e389
--- /dev/null
+++ b/scripts/pathview_install.py
@@ -0,0 +1,70 @@
+"""Shared package-install primitives for the Pyodide and Flask backends.
+
+Single source of truth for "is this importable?" + "install this package",
+used by BOTH the engine-install seam (worker boot, via engineInstall.ts) and
+the runtime toolbox installer (via TOOLBOX_PYTHON_HELPERS). Defined here, in
+one place, so there is exactly one micropip / pip code path with one
+error-classification scheme instead of three inline copies.
+
+The engine seam injects this before the worker snapshots ``_clean_globals``,
+so these names survive a simulation reset; the toolbox layer re-injects the
+same source (idempotent) on demand.
+"""
+
+import sys as _pv_sys
+import importlib as _pv_importlib
+
+
+def _pv_already_installed(import_path):
+    """Return True if the given module path is already importable."""
+    if not import_path:
+        return False
+    try:
+        _pv_importlib.import_module(import_path)
+        return True
+    except Exception:
+        return False
+
+
+async def _pv_install_micropip(spec, pre=False, keep_going=True):
+    """Pyodide-side install via micropip (top-level await).
+
+    micropip can only install pure-Python wheels (or packages Pyodide ships
+    pre-built), so toolboxes with compiled/native code fail here even though
+    they install fine in the standalone (pip-backed) build. On failure we
+    classify the error and prefix it with PV_INCOMPATIBLE (browser-runtime
+    limitation) or PV_INSTALL_ERROR (genuine failure) so the JS side can show
+    a useful hint instead of a raw traceback.
+
+    ``pre`` allows pre-release wheels (used by the engine seam); ``keep_going``
+    keeps resolving the rest of the dependency set after a single miss.
+    """
+    import micropip
+    try:
+        await micropip.install(spec, keep_going=keep_going, pre=pre)
+    except Exception as e:
+        msg = str(e)
+        low = msg.lower()
+        incompatible = (
+            "pure python" in low
+            or "can't find" in low
+            or "cannot find" in low
+            or "no matching distribution" in low
+            or "no known package" in low
+        )
+        tag = "PV_INCOMPATIBLE" if incompatible else "PV_INSTALL_ERROR"
+        raise RuntimeError(tag + ": " + msg)
+    return {"ok": True, "spec": spec, "via": "micropip"}
+
+
+def _pv_install_pip(spec):
+    """CPython-side install via subprocess pip (Flask backend)."""
+    import subprocess as _pv_subprocess
+    res = _pv_subprocess.run(
+        [_pv_sys.executable, "-m", "pip", "install", spec],
+        capture_output=True,
+        text=True,
+    )
+    if res.returncode != 0:
+        raise RuntimeError("pip install failed:\n" + (res.stderr or res.stdout))
+    return {"ok": True, "spec": spec, "via": "pip"}
diff --git a/src/lib/pyodide/backend/pyodide/engineInstall.ts b/src/lib/pyodide/backend/pyodide/engineInstall.ts
index cbd7f4ad..4e73f8d2 100644
--- a/src/lib/pyodide/backend/pyodide/engineInstall.ts
+++ b/src/lib/pyodide/backend/pyodide/engineInstall.ts
@@ -10,6 +10,7 @@
 
 import { PYTHON_PACKAGES } from '$lib/constants/dependencies';
 import { PROGRESS_MESSAGES } from '$lib/constants/messages';
+import INSTALL_PY from '../../../../../scripts/pathview_install.py?raw';
 import type { PyodideInterface } from 'https://cdn.jsdelivr.net/pyodide/v0.29.4/full/pyodide.mjs';
 
 export interface EngineInstallContext {
@@ -23,6 +24,12 @@ export async function installEngine(
 	pyodide: PyodideInterface,
 	ctx: EngineInstallContext
 ): Promise<void> {
+	// Define the shared install primitive (`_pv_install_micropip`) that the
+	// toolbox layer also uses (via TOOLBOX_PYTHON_HELPERS). Injected here, before
+	// the worker snapshots `_clean_globals`, so it survives a simulation reset —
+	// one micropip code path with one error-classification scheme, not two.
+	await pyodide.runPythonAsync(INSTALL_PY);
+
 	for (const pkg of PYTHON_PACKAGES) {
 		const progressKey = `INSTALLING_${pkg.import.toUpperCase()}` as keyof typeof PROGRESS_MESSAGES;
 		ctx.send({
@@ -31,11 +38,9 @@ export async function installEngine(
 		});
 
 		try {
-			const preFlag = pkg.pre ? ', pre=True' : '';
-			await pyodide.runPythonAsync(`
-import micropip
-await micropip.install('${pkg.pip}'${preFlag})
-			`);
+			await pyodide.runPythonAsync(
+				`await _pv_install_micropip('${pkg.pip}', pre=${pkg.pre ? 'True' : 'False'})`
+			);
 
 			// Verify installation
 			await pyodide.runPythonAsync(`
diff --git a/src/lib/toolbox/python.ts b/src/lib/toolbox/python.ts
index 22c368fa..1749013a 100644
--- a/src/lib/toolbox/python.ts
+++ b/src/lib/toolbox/python.ts
@@ -13,6 +13,7 @@
  */
 
 import INTROSPECT_PY from '../../../scripts/pathview_introspect.py?raw';
+import INSTALL_PY from '../../../scripts/pathview_install.py?raw';
 
 const RUNTIME_GLUE = `
 import sys as _pv_sys
@@ -22,57 +23,6 @@ import types as _pv_types
 _PV_INLINE_PREFIX = "pathview_inline_"
 
 
-def _pv_already_installed(import_path):
-    """Return True if the given module path is already importable."""
-    if not import_path:
-        return False
-    try:
-        _pv_importlib.import_module(import_path)
-        return True
-    except Exception:
-        return False
-
-
-async def _pv_install_micropip(spec):
-    """Pyodide-side install via micropip (top-level await).
-
-    micropip can only install pure-Python wheels (or packages Pyodide
-    ships pre-built), so toolboxes with compiled/native code fail here
-    even though they install fine in the standalone (pip-backed) build.
-    On failure we classify the error and prefix it with PV_INCOMPATIBLE
-    (browser-runtime limitation) or PV_INSTALL_ERROR (genuine failure)
-    so the JS side can show a useful hint instead of a raw traceback."""
-    import micropip
-    try:
-        await micropip.install(spec, keep_going=True)
-    except Exception as e:
-        msg = str(e)
-        low = msg.lower()
-        incompatible = (
-            "pure python" in low
-            or "can't find" in low
-            or "cannot find" in low
-            or "no matching distribution" in low
-            or "no known package" in low
-        )
-        tag = "PV_INCOMPATIBLE" if incompatible else "PV_INSTALL_ERROR"
-        raise RuntimeError(tag + ": " + msg)
-    return {"ok": True, "spec": spec, "via": "micropip"}
-
-
-def _pv_install_pip(spec):
-    """CPython-side install via subprocess pip (Flask backend)."""
-    import subprocess as _pv_subprocess
-    res = _pv_subprocess.run(
-        [_pv_sys.executable, "-m", "pip", "install", spec],
-        capture_output=True,
-        text=True,
-    )
-    if res.returncode != 0:
-        raise RuntimeError("pip install failed:\\n" + (res.stderr or res.stdout))
-    return {"ok": True, "spec": spec, "via": "pip"}
-
-
 def _pv_load_inline(module_name, code):
     """Exec a single-file Python module string into sys.modules."""
     if not module_name.startswith(_PV_INLINE_PREFIX):
@@ -178,7 +128,7 @@ def _pv_module_version(import_path):
 _pv_helpers_loaded = True
 `;
 
-export const TOOLBOX_PYTHON_HELPERS = INTROSPECT_PY + RUNTIME_GLUE;
+export const TOOLBOX_PYTHON_HELPERS = INTROSPECT_PY + INSTALL_PY + RUNTIME_GLUE;
 
 /** Sentinel expression used to check whether helpers are already loaded in the REPL. */
 export const TOOLBOX_HELPERS_SENTINEL = `'_pv_helpers_loaded' in dir()`;