diff --git a/CLAUDE.md b/CLAUDE.md
index 3b7af17..51a4090 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -71,6 +71,6 @@ Worker messages:
 - **Console and Stop:** output, REPL inputs, Tests reports and notes form one transcript (`ConsoleEntry` list after `output`). While Python is busy for more than `STOP_BUTTON_DELAY`, the run button is **Stop**: `stopPython` terminates the worker and calls `startWorker` again, so the REPL namespace is gone after a stop. The embed reports this to its parent (protocol version 4, `glpython:busy`/`glpython:stop`).
 - **UI strings** come in via the `t: CoreStrings` prop. `src/i18n.ts` is their single source: `coreStrings` holds German and English, and `resolveUiLocale` picks the language. The embed uses them directly; the glpython IDE imports them and adds only its shell strings. New strings have been added as *optional* `CoreStrings` keys with an English fallback, so older hosts keep compiling; add both languages to `coreStrings`. Python values, reprs and error messages are never translated.
 - **Two layouts:** with `compact` (the embed) the original tree (`main-split` > `editor-column` + graphics aside), unchanged and styled by `src/embed/style.css`; without it (the IDE) the stacked layout (`workspace-stack`: `stack-top` with the editor panel and, while drawing, the graphics, then `stack-divider` and `stack-console`). Both are assembled from the same JSX pieces (`actionsNode`, `visualizerBarNode`, `editorWrapNode`, `consoleNode`, …) just before the return. The buttons can be portaled into the host's bar (`actionsContainer`).
-- **Embedded/reduced layouts:** the knobs are `compact`, `capabilities` (`WorkspaceCapabilities`, including `repl`) and `command` (`WorkspaceCommand`, an immutable `{id, type}` used by editor-free hosts to trigger run/visualize). Defaults must preserve the full-workspace behavior.
+- **Embedded/reduced layouts:** the knobs are `compact`, `capabilities` (`WorkspaceCapabilities`, including `repl`) and `command` (`WorkspaceCommand`, an immutable `{id, type}` used by hosts to trigger run/visualize/test/stop/reset without the workspace's own buttons; `reset` restarts Python and clears the console). Defaults must preserve the full-workspace behavior.
 
 **Embed protocol.** `src/embedProtocol.ts` defines the versioned message types and validators (`parseParentMessage`, `parseParentOrigin`, `GLPYTHON_EMBED_PROTOCOL_VERSION`, `GLPYTHON_MAX_SOURCE_LENGTH`), all re-exported from `src/index.ts`. The iframe (`src/embed/App.tsx`) requires an exact `parentOrigin` query param, sends `glpython:ready`/`glpython:resize`, and accepts `glpython:load`/`run`/`visualize`/`reset`. `run`/`visualize` carry the source snapshot so the parent remains the authoritative editor. Version 2 adds `files` + `mainFile` for programs of several files, version 3 adds `glpython:test` (doctests); version 4 adds `glpython:stop` and `glpython:busy`; the embed still accepts every earlier version and answers each parent in the version it last used, so older (e.g. cached) macros keep working. Modes: `eval` (with REPL), `turtle` (graphics layout), `visual` (visualizer-only, cannot exit). Reset remounts the workspace via a `key` generation counter, which also recreates the worker. Any protocol change should bump/handle the version and be covered in `scripts/check-embed-protocol.mjs`; also update `embed/demo.html` and the README.
diff --git a/README.md b/README.md
index 4d26f46..582bbfe 100644
--- a/README.md
+++ b/README.md
@@ -188,7 +188,8 @@ a visualization), the run button becomes **Stop** (`stop`: «Stoppen»). Stoppin
 ends Python's worker and starts a new one: the code stays, the console keeps
 what was printed and adds `stoppedNote`, and the REPL starts in an empty
 namespace (earlier entries can't be visualized anymore). Hosts can stop with
-the command `{ id, type: 'stop' }`, and learn when Python is busy through the
+the command `{ id, type: 'stop' }` (and restart Python with an empty console,
+as Reset does, with `{ id, type: 'reset' }`), and learn when Python is busy through the
 `onBusyChange` prop.
 
 ### REPL
diff --git a/package.json b/package.json
index 01e9eeb..a91ef07 100644
--- a/package.json
+++ b/package.json
@@ -26,7 +26,7 @@
     "preview:embed": "vite preview --config vite.embed.config.ts",
     "test:protocol": "npm run build && node scripts/check-embed-protocol.mjs",
     "test:hints": "node scripts/check-error-hints.mjs",
-    "test:runtime": "python3 -B scripts/check-runtime-columns.py && python3 -B scripts/check-runtime-values.py && python3 -B scripts/check-runtime-doctests.py && python3 -B scripts/check-runtime-calls.py && python3 -B scripts/check-runtime-hints.py && python3 -B scripts/check-runtime-fidelity.py && python3 -B scripts/check-runtime-replay.py",
+    "test:runtime": "python3 -B scripts/check-runtime-columns.py && python3 -B scripts/check-runtime-values.py && python3 -B scripts/check-runtime-doctests.py && python3 -B scripts/check-runtime-calls.py && python3 -B scripts/check-runtime-hints.py && python3 -B scripts/check-runtime-fidelity.py && python3 -B scripts/check-runtime-replay.py && python3 -B scripts/check-runtime-imports.py",
     "prepare": "npm run build"
   },
   "peerDependencies": {
diff --git a/scripts/check-runtime-imports.py b/scripts/check-runtime-imports.py
new file mode 100644
index 0000000..be3650a
--- /dev/null
+++ b/scripts/check-runtime-imports.py
@@ -0,0 +1,85 @@
+"""Regression test: Run (and Tests, Visualize) imports the project's files as
+they are now. A changed file is read again - also when its size stays the
+same and it changes within a second - a new file is found, and a removed or
+renamed file can't be imported under its old name anymore, as in CPython
+(ModuleNotFoundError) - before, its old module stayed in memory.
+
+session.py's _glpython_invalidate_modules gets the paths of the files mounted
+now, as the worker's mountProjectFiles passes them, and remembers those of the
+time before itself.
+
+Runs the runtime with CPython (no Pyodide needed):
+    python3 -B scripts/check-runtime-imports.py
+"""
+import json
+import os
+import sys
+import tempfile
+
+ROOT = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+RUNTIME = os.path.join(ROOT, "src", "runtime")
+
+runtime = {"__name__": "glpython_runtime"}
+for name in ("hints.py", "session.py"):
+    with open(os.path.join(RUNTIME, name), encoding="utf-8") as handle:
+        exec(compile(handle.read(), "<exec>", "exec"), runtime)
+
+folder = tempfile.mkdtemp(prefix="glpython-imports-")
+sys.path.insert(0, folder)
+mounted = []
+failures = []
+
+
+def mount(files):
+    """As the worker's mountProjectFiles: remove the old files, write the new
+    ones, pass the new ones' paths."""
+    global mounted
+    for name in mounted:
+        os.remove(os.path.join(folder, name))
+    for name, source in files.items():
+        with open(os.path.join(folder, name), "w", encoding="utf-8") as handle:
+            handle.write(source)
+    mounted = list(files)
+    runtime["_glpython_invalidate_modules"](json.dumps([os.path.join(folder, name) for name in mounted]))
+
+
+def run(main):
+    namespace = {"__name__": "__main__"}
+    try:
+        exec(main, namespace)
+        return namespace.get("result")
+    except BaseException as error:
+        return f"{type(error).__name__}: {error}"
+
+
+def expect(label, got, want):
+    if got != want:
+        failures.append(f"{label}: got {got!r}, want {want!r}")
+
+
+MAIN = "import helfer\nresult = helfer.wert()\n"
+mount({"main.py": MAIN, "helfer.py": "def wert():\n    return 1\n"})
+expect("first run", run(MAIN), 1)
+mount({"main.py": MAIN, "helfer.py": "def wert():\n    return 2\n"})
+expect("same size, at once", run(MAIN), 2)
+mount({"main.py": MAIN, "helfer.py": "def wert():\n    return 3\n"})
+expect("same size, at once again", run(MAIN), 3)
+mount({"main.py": MAIN, "helfer.py": "def wert():\n    return 40\n"})
+expect("other size", run(MAIN), 40)
+mount({"main.py": "import neu\nresult = neu.X\n", "neu.py": "X = 5\n"})
+expect("a new file", run("import neu\nresult = neu.X\n"), 5)
+mount({"main.py": MAIN})
+expect("helfer.py removed", run(MAIN), "ModuleNotFoundError: No module named 'helfer'")
+mount({"main.py": MAIN, "helfer2.py": "def wert():\n    return 7\n"})
+expect("renamed to helfer2.py, imported as helfer2", run("import helfer2\nresult = helfer2.wert()\n"), 7)
+expect("renamed, imported under the old name", run(MAIN), "ModuleNotFoundError: No module named 'helfer'")
+# A module importing another project file (parser.py next to auswerter.py).
+mount({"main.py": "import auswerter\nresult = auswerter.auswerten()\n", "auswerter.py": "from parser import parse\ndef auswerten():\n    return parse()\n", "parser.py": "def parse():\n    return 'alt'\n"})
+expect("parser via auswerter", run("import auswerter\nresult = auswerter.auswerten()\n"), "alt")
+mount({"main.py": "import auswerter\nresult = auswerter.auswerten()\n", "auswerter.py": "from parser import parse\ndef auswerten():\n    return parse()\n", "parser.py": "def parse():\n    return 'neu'\n"})
+expect("changed parser via auswerter", run("import auswerter\nresult = auswerter.auswerten()\n"), "neu")
+
+if failures:
+    print("\n".join(failures))
+    sys.exit(f"{len(failures)} import check(s) failed.")
+print("Runtime import checks passed.")
diff --git a/src/GlPythonWorkspace.tsx b/src/GlPythonWorkspace.tsx
index fd58056..eade513 100644
--- a/src/GlPythonWorkspace.tsx
+++ b/src/GlPythonWorkspace.tsx
@@ -1242,13 +1242,9 @@ function GlPythonWorkspace(props: GlPythonWorkspaceProps) {
       runTests()
     }
     if (command.type === 'stop') stopPython()
-    if (command.type === 'reset') {
-      exitVisualizer()
-      setConsoleEntries([])
-      setOutput(t.readyOutput)
-      setOutputErrorHint(null)
-      setGraphics([])
-    }
+    // Restarts Python and clears the console, as the Reset button does (the
+    // IDE's «Python neu starten» in its menu).
+    if (command.type === 'reset') resetPython()
     // Commands are immutable events. Their id, rather than render-time callback
     // identities, determines whether the effect should run again.
     // eslint-disable-next-line react-hooks/exhaustive-deps
diff --git a/src/runtime/session.py b/src/runtime/session.py
index bbbebb2..65bcc5c 100644
--- a/src/runtime/session.py
+++ b/src/runtime/session.py
@@ -25,12 +25,25 @@ def _glpython_error_message(error):
   text = error.msg if isinstance(error, SyntaxError) and error.msg else str(error)
   return f"{type(error).__name__}: {text}" if text else type(error).__name__
 
+# Run, Tests and Visualize import the project's files as they are now: the
+# modules of every file mounted now and at the time before are dropped, so a
+# changed file is read again and a removed or renamed one can't be imported
+# under its old name anymore (as in CPython: ModuleNotFoundError) - its old
+# module used to stay. The import system's directory caches are cleared too,
+# and no bytecode is written, so a file changed within the same second keeps
+# no stale .pyc.
+sys.dont_write_bytecode = True
+_glpython_mounted_paths = set()
+
 def _glpython_invalidate_modules(mounted_paths_json):
-  for mounted_path in json.loads(mounted_paths_json):
-    for module_name in list(sys.modules):
-      module = sys.modules[module_name]
-      if getattr(module, "__file__", None) == mounted_path:
-        del sys.modules[module_name]
+  global _glpython_mounted_paths
+  import importlib
+  mounted_paths = set(json.loads(mounted_paths_json))
+  for module_name in list(sys.modules):
+    if getattr(sys.modules[module_name], "__file__", None) in mounted_paths | _glpython_mounted_paths:
+      del sys.modules[module_name]
+  _glpython_mounted_paths = mounted_paths
+  importlib.invalidate_caches()
 
 # Python's traceback for an error the program raised, as CPython prints it
 # (carets, chained exceptions, a SyntaxError's caret line), without this