flatpak: run host interpreters via flatpak-spawn; validation --mode flag

py_func, lua_func and the run item now reach host binaries through
`flatpak-spawn --host` instead of trying to load them under the
sandbox runtime (which fails with a glibc ABI mismatch). Adds
`--talk-name=org.freedesktop.Flatpak` to the manifest, stages the
/app/lib/testium tree under /tmp so the host can read it, and drops
the dead `_FLATPAK_HOST_DIRS` / lib-injection code paths that the
new approach makes obsolete.

Validation suite gains a `--mode source|wheel|pyinstaller|flatpak|
appimage` flag so the same item set can run against every packaging
channel; per-mode report file names avoid clobbering.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

DESIGN.md

@@ -114,11 +114,20 @@ To add a new API call usable from subprocesses:
 ### External interpreter resolution (`bins.py`)
 `src/testium/interpreter/utils/bins.py` — single source of truth for the paths to the external Python and Lua interpreters used by subprocesses.
 
-- `python_bin()` / `lua_bin()` : resolve once, cache in memory. User can override via the `python_bin` / `lua_bin` global dict keys (typically populated from the YAML config). Falls back to discovery on PATH (candidates: `python3`/`python` and `lua`/`lua5.5`/`lua5.4`/`lua5.3`/`lua5.2`/`lua5.1`).
+- `python_bin()` / `lua_bin()` : resolve and cache. The cache is keyed by `(name, override)` so that a later change to `gd[python_bin]` (typically when a `param.yaml` sets the key) triggers a re-resolution on the next lookup instead of returning the stale auto-discovered path. Falls back to discovery on PATH (candidates: `python3`/`python` and `lua`/`lua5.5`/`lua5.4`/`lua5.3`/`lua5.2`/`lua5.1`).
 - `ensure(*names)` : called by `TestSet._validate_runtime_deps()` at test load. Always requires `python` (the eval engine always runs); requires `lua` only if a `lua_func` item is in the tree. Fails fast with a clear error citing tried candidates and override key.
 
 Engines (`PyProcessBase`, `LuaProcessBase`, `EvalExecEngine`) call `bins.python_bin()`/`bins.lua_bin()` themselves — call sites never pass an explicit binary path.
 
+#### Override-timing contract (`apply_overrides`)
+`bins.python_bin()` is called for the **first** time inside `eval_process_init()` (the long-lived inline-`<| … |>` subprocess), which happens **before** the YAML param files are loaded. To make `-d python_bin=…` and the GUI `python_bin` preference take effect for `eval_proc` itself, `process.py:run()` applies them to gd **before** `eval_process_init()` via the `apply_overrides()` helper extracted from `update_global()`. The post-load `update_global()` call then re-applies the same overrides (after `prepare_global()` clears gd), keeping the gd value in sync with the cached resolution.
+
+| Override source | `eval_proc` | `py_func` / `cycle` / `post_exec` |
+|---|---|---|
+| `-d python_bin=…` (CLI) | ✅ | ✅ |
+| GUI `python_bin` preference | ✅ | ✅ |
+| `python_bin: …` in `param.yaml` | ❌ (eval_proc already started) | ✅ (cache re-resolves on key change) |
+
 ## Key files
 
 | Path | Role |
@@ -261,12 +270,18 @@ Both Flatpak and AppImage export `TESTIUM_VERSION` from a launcher (Flatpak: lau
 - `unittest` item: renamed from `unittest_file`.
 - GUI test tree: check and fold state preserved across same-file reloads.
 - Licence: EUPL-1.2.
+- Interpreter override timing: `apply_overrides()` extracted from `update_global()` and called by `process.py:run()` before `eval_process_init()`, so `-d python_bin=…` / GUI prefs reach `bins.python_bin()` on its first lookup. `bins._resolve()` cache is now keyed by `(name, override)` so later `param.yaml` changes are picked up by subsequently constructed engines.
 
 ## Validation tests
-Located in `test/validation/`. Run with `-b` flag:
+Located in `test/validation/`. Two entry points:
 ```
-./run.sh -b -- test/validation/main.tum
+./test/validation/run.sh        # wrapper — uses a dedicated venv (see below)
+./run.sh -b -- test/validation/main.tum   # direct — testium's own python is used for test execution
 ```
+The `run.sh` / `run.bat` wrappers create a dedicated Python venv at `${TMPDIR:-/tmp}/testium-validation-venv` (Linux) or `%TEMP%\testium-validation-venv` (Windows), with `--system-site-packages` + `pip install junit-xml`, and run the suite with `-d python_bin=…` so every test-execution subprocess (eval_proc, py_func, cycle, post_exec) runs inside the venv. testium itself keeps running in the project's own environment. `clean` as the first argument recreates the venv.
+
+The `venv` item (`test/validation/items/venv/`) asserts that the override actually took effect: `python_bin` is set, `sys.executable` matches it, `sys.prefix == dirname(dirname(python_bin))`, and `sys.prefix != sys.base_prefix` (the last marker catches the case where `python_bin` happens to be a system interpreter, which path-equality alone would miss because the venv's `bin/python3` is a symlink to the host). Both `eval_proc` (inline `<| … |>`) and `py_func` paths are exercised.
+
 Parallel item tests: `test/validation/items/parallel/test.tum`
 
 ## Dependencies

build_all.sh

@@ -8,6 +8,9 @@
 # release_note.txt is copied to dist/ up front (with a warning if it has no
 # entry for the current version).
 #
+# By default, a step is skipped if its artifact already exists in dist/.
+# Pass --clean to remove existing dist/ artifacts and rebuild everything.
+#
 # All artifacts are collected (copied) under <repo>/dist/. Original outputs in
 # src/dist/, package/*/dist/, doc/manual/ are left in place. Wheel and AppImage
 # keep their original names (which already contain the version); manual,
@@ -15,17 +18,35 @@
 #
 # Re-uses scripts/build_env.sh and scripts/set_env.sh — the same pair invoked
 # by run.sh — so the venv at test/tmp/.venv stays the single source of Python
-# dependencies. `build` and `pyinstaller` are installed into that venv on
-# demand if not already there. Flatpak and AppImage build in their own
-# container/sandbox; their build.sh scripts have their own toolchain checks.
+# dependencies. `build`, `pyinstaller`, `sphinx` and `linuxdoc` are installed
+# into that venv on demand if not already there. Flatpak and AppImage build in
+# their own container/sandbox; their build.sh scripts have their own toolchain
+# checks.
 
 set -e
 
+CLEAN=0
+for arg in "$@"; do
+    case "$arg" in
+        --clean|-c) CLEAN=1 ;;
+        *) echo "Unknown option: $arg" >&2; exit 1 ;;
+    esac
+done
+
 SCRIPT_DIR=$(realpath "$(dirname "$0")")
 VERSION=$(cat "$SCRIPT_DIR/src/VERSION")
 DIST_DIR="$SCRIPT_DIR/dist"
 mkdir -p "$DIST_DIR"
 
+if [ "$CLEAN" -eq 1 ]; then
+    echo "-- clean: removing existing dist artifacts for version $VERSION"
+    rm -f "$DIST_DIR/testium-manual-${VERSION}.pdf"
+    rm -f "$DIST_DIR"/testium-${VERSION}-*.whl
+    rm -f "$DIST_DIR/testium-${VERSION}"
+    rm -f "$DIST_DIR/testium-${VERSION}.flatpak"
+    rm -f "$DIST_DIR"/Testium-${VERSION}-*.AppImage
+fi
+
 # Release note: copy it to dist/ and warn (but don't fail) if it has no entry
 # for the current version.
 RELEASE_NOTE_SRC="$SCRIPT_DIR/release_note.txt"
@@ -42,9 +63,6 @@ export REQ_PATH="$SCRIPT_DIR/src/requirements.txt"
 bash "$SCRIPT_DIR/scripts/build_env.sh"
 source "$SCRIPT_DIR/scripts/set_env.sh"
 
-# Ensure wheel/PyInstaller toolchains are present in the venv.
-python -m pip install --quiet --upgrade build pyinstaller
-
 step() {
     echo
     echo "================================================================"
@@ -52,51 +70,90 @@ step() {
     echo "================================================================"
 }
 
+skip() { echo "  (already built — skipping)"; }
+
 # 1. Manual PDF
-step "1/5  Manual PDF (version $VERSION)"
-bash "$SCRIPT_DIR/doc/manual/sphinx/build_doc.sh"
-MANUAL_SRC="$SCRIPT_DIR/doc/manual/testium_manual.pdf"
 MANUAL="$DIST_DIR/testium-manual-${VERSION}.pdf"
-cp -f "$MANUAL_SRC" "$MANUAL"
+step "1/5  Manual PDF (version $VERSION)"
+if [ ! -f "$MANUAL" ]; then
+    python -m pip install --quiet --upgrade sphinx linuxdoc
+    bash "$SCRIPT_DIR/doc/manual/sphinx/build_doc.sh"
+    cp -f "$SCRIPT_DIR/doc/manual/testium_manual.pdf" "$MANUAL"
+else
+    skip
+fi
 
 # 2. Wheel — PEP 427 name kept (already contains version)
 step "2/5  Wheel (version $VERSION)"
-(
-    cd "$SCRIPT_DIR/src"
-    rm -rf dist build *.egg-info
-    python -m build --wheel
-)
-WHEEL_SRC=$(ls -1t "$SCRIPT_DIR/src/dist"/*.whl | head -1)
-WHEEL="$DIST_DIR/$(basename "$WHEEL_SRC")"
-cp -f "$WHEEL_SRC" "$WHEEL"
+WHEEL=$(ls -1t "$DIST_DIR"/testium-${VERSION}-*.whl 2>/dev/null | head -1)
+if [ -z "$WHEEL" ]; then
+    python -m pip install --quiet --upgrade build
+    (
+        cd "$SCRIPT_DIR/src"
+        rm -rf dist build *.egg-info
+        python -m build --wheel
+    )
+    WHEEL_SRC=$(ls -1t "$SCRIPT_DIR/src/dist"/*.whl | head -1)
+    WHEEL="$DIST_DIR/$(basename "$WHEEL_SRC")"
+    cp -f "$WHEEL_SRC" "$WHEEL"
+else
+    skip
+fi
 
 # 3. PyInstaller binary
-step "3/5  PyInstaller binary (version $VERSION)"
-bash "$SCRIPT_DIR/package/pyinstaller/build.sh"
-PYI_SRC="$SCRIPT_DIR/package/pyinstaller/dist/testium"
 PYI_BIN="$DIST_DIR/testium-${VERSION}"
-cp -f "$PYI_SRC" "$PYI_BIN"
+step "3/5  PyInstaller binary (version $VERSION)"
+if [ ! -f "$PYI_BIN" ]; then
+    python -m pip install --quiet --upgrade pyinstaller
+    bash "$SCRIPT_DIR/package/pyinstaller/build.sh"
+    cp -f "$SCRIPT_DIR/package/pyinstaller/dist/testium" "$PYI_BIN"
+else
+    skip
+fi
 
 # 4. Flatpak bundle
-step "4/5  Flatpak bundle (version $VERSION)"
-(
-    cd "$SCRIPT_DIR/package/flatpak"
-    bash build.sh
-)
-FLATPAK_SRC="$SCRIPT_DIR/package/flatpak/testium.flatpak"
 FLATPAK_BUNDLE="$DIST_DIR/testium-${VERSION}.flatpak"
-cp -f "$FLATPAK_SRC" "$FLATPAK_BUNDLE"
+step "4/5  Flatpak bundle (version $VERSION)"
+if [ ! -f "$FLATPAK_BUNDLE" ]; then
+    FLATPAK_DEPS=(
+        "org.kde.Platform//6.10"
+        "org.kde.Sdk//6.10"
+        "io.qt.PySide.BaseApp//6.10"
+    )
+    if ! flatpak remotes --user | grep -q "^flathub"; then
+        echo "  Adding Flathub remote"
+        flatpak remote-add --user --if-not-exists flathub https://dl.flathub.org/repo/flathub.flatpakrepo
+    fi
+    for dep in "${FLATPAK_DEPS[@]}"; do
+        if ! flatpak info --user "$dep" &>/dev/null && ! flatpak info --system "$dep" &>/dev/null; then
+            echo "  Installing Flatpak dependency: $dep"
+            flatpak install --user --noninteractive flathub "$dep"
+        fi
+    done
+    (
+        cd "$SCRIPT_DIR/package/flatpak"
+        bash build.sh
+    )
+    cp -f "$SCRIPT_DIR/package/flatpak/testium.flatpak" "$FLATPAK_BUNDLE"
+else
+    skip
+fi
 
 # 5. AppImage
 step "5/5  AppImage (version $VERSION)"
-(
-    cd "$SCRIPT_DIR/package/appimage"
-    bash build.sh
-)
-APPIMAGE_SRC=$(ls -1t "$SCRIPT_DIR/package/appimage"/*.AppImage 2>/dev/null | head -1)
-APPIMAGE="$DIST_DIR/$(basename "$APPIMAGE_SRC")"
-cp -f "$APPIMAGE_SRC" "$APPIMAGE"
-chmod +x "$APPIMAGE"
+APPIMAGE=$(ls -1t "$DIST_DIR"/Testium-${VERSION}-*.AppImage 2>/dev/null | head -1)
+if [ -z "$APPIMAGE" ]; then
+    (
+        cd "$SCRIPT_DIR/package/appimage"
+        bash build.sh
+    )
+    APPIMAGE_SRC=$(ls -1t "$SCRIPT_DIR/package/appimage"/*.AppImage 2>/dev/null | head -1)
+    APPIMAGE="$DIST_DIR/$(basename "$APPIMAGE_SRC")"
+    cp -f "$APPIMAGE_SRC" "$APPIMAGE"
+    chmod +x "$APPIMAGE"
+else
+    skip
+fi
 
 step "All packages built"
 printf "  manual       : %s\n" "$MANUAL"

package/flatpak/org.testium.Testium.yaml

@@ -16,6 +16,11 @@ finish-args:
   - --filesystem=home
   - --filesystem=/tmp
   - --filesystem=host-os
+  # Allow flatpak-spawn --host to launch host binaries (Python, Lua, git…)
+  # outside the sandbox. Required because the sandbox glibc/ABI is
+  # incompatible with arbitrary host shared libraries — we route py_func and
+  # lua_func through the host instead.
+  - --talk-name=org.freedesktop.Flatpak
 
 build-options:
   build-args:

release_note.txt

@@ -1,3 +1,30 @@
+version 0.1.3
+==============
+- Stop interrupts engaged blocking steps (console, py_func, lua_func,
+  json_rpc, sleep) within ~200 ms instead of waiting for the step
+  to finish.
+- GUI Start / Stop / Pause flow simplified.
+- lua_func: a function returning nil is no longer reported as a failure.
+- ``-d python_bin=...`` and the GUI ``python_bin`` preference now reach
+  the eval subprocess (used to be silently ignored). ``param.yaml`` can
+  also override ``python_bin`` for py_func / cycle / post_exec.
+- Validation suite: ``test/validation/run.sh`` (and ``run.bat``)
+  runs the suite inside a dedicated venv in the system temp dir.
+- build_all.sh: ``release_note.txt`` and the user manual copied into
+  ``dist/``; warning if the file has no entry for the version being built.
+- Flatpak: every GUI file/directory dialog (open test, save report, log
+  path, default report/log dirs, python/lua interpreter pickers) now
+  bypasses the XDG document portal — the v0.1.2 fix was only on the
+  "open test" dialog.
+- Flatpak: py_func / lua_func / run sub-instance now execute on the host
+  via flatpak-spawn, lifting the previous glibc/ABI incompatibility that
+  prevented user-configured host Python or Lua interpreters from being
+  reached from the sandbox.
+- Validation suite: single entry point with ``--mode source|wheel|
+  pyinstaller|flatpak|appimage`` to validate any packaging channel
+  against the same item set; reports are stamped per mode.
+- GUI: the "Run tum" test item now uses the testium logo.
+
 version 0.1.2
 ==============
 - Flatpak: opening a test from the GUI now correctly finds its companion

src/VERSION

@@ -1 +1 @@
-0.1.2
+0.1.3

src/testium/interpreter/process.py

@@ -16,6 +16,7 @@ from interpreter.utils.test_init import (
     env_init,
     prepare_global,
     update_global,
+    apply_overrides,
     set_standard_gd_keys,
     test_run_init,
     test_run_header,
@@ -210,6 +211,19 @@ class TestProcess(Process):
 
                 env_init()
 
+                # Apply GUI defaults and CLI defines to the global dict
+                # *before* eval_proc starts: bins.python_bin() reads
+                # ``python_bin`` from gd on its very first call (during
+                # eval_process_init) and caches the result. Without this,
+                # ``-d python_bin=...`` and the GUI ``python_bin`` preference
+                # would only take effect for items spawned *after* the cache
+                # was already populated with the auto-discovered interpreter,
+                # i.e. they would silently be ignored for eval_proc itself.
+                # _load_initial_params re-applies the same overrides after
+                # ``prepare_global()`` clears gd, so the gd value stays in
+                # sync with the cached path.
+                apply_overrides(self.__defs, self.__gui_defaults)
+
                 # Creation of the python evaluation process for loading of the complete test
                 eval_proc = eval_process_init(api_request, 10, test_dir)
                 eval_proc.start()

src/testium/interpreter/test_items/test_item_run.py

@@ -24,9 +24,15 @@ def _testium_launch_cmd():
     appimage = os.environ.get("APPIMAGE")
     if appimage:
         return [appimage]
-    # Flatpak: re-launch via the Flatpak app id.
+    # Flatpak: re-launch via the Flatpak app id, but on the host side —
+    # the `flatpak` CLI cannot run inside our sandbox (no D-Bus access to the
+    # host Flatpak service, and the host binary would need host libs that are
+    # ABI-incompatible with the sandbox runtime). flatpak-spawn proxies the
+    # call to the host via org.freedesktop.Flatpak (allowed by --talk-name in
+    # the manifest).
     if os.path.isfile("/.flatpak-info"):
-        return ["flatpak", "run", "org.testium.Testium"]
+        return ["flatpak-spawn", "--host",
+                "flatpak", "run", "org.testium.Testium"]
     # PyInstaller frozen exe: sys.executable is the binary itself.
     if getattr(sys, "frozen", False):
         return [sys.executable]

src/testium/interpreter/utils/bins.py

@@ -17,8 +17,11 @@ Public API
 ``reset()``             : clear the cache (mostly useful for tests)
 """
 
+import atexit
 import os
+import shutil
 import subprocess
+import tempfile
 
 import api.testium as tm
 from interpreter.utils.paths import sys_app_path_lin, sys_app_path_win
@@ -30,20 +33,6 @@ from runtime.tum_except import ETUMRuntimeError
 _PYTHON_CANDIDATES = ["python3", "python"]
 _LUA_CANDIDATES = ["lua", "lua5.5", "lua5.4", "lua5.3", "lua5.2", "lua5.1"]
 
-# When running inside a Flatpak, --filesystem=host-os mounts the host at
-# /run/host (read-only). Binaries and libraries from the host are not on the
-# sandbox PATH/LD_LIBRARY_PATH, so we probe and inject them explicitly.
-_FLATPAK_HOST_DIRS = [
-    "/run/host/usr/local/bin",
-    "/run/host/usr/bin",
-    "/run/host/bin",
-]
-_FLATPAK_HOST_LIB_DIRS = [
-    "/run/host/usr/lib",
-    "/run/host/usr/lib64",
-    "/run/host/usr/local/lib",
-]
-
 # Inside an AppImage, AppRun prepends $APPDIR/usr/bin to PATH and exports a
 # bundle-local PYTHONHOME / PYTHONPATH / LD_LIBRARY_PATH. We want py_func and
 # lua_func to run under the *host* interpreter (not the bundled one), so we
@@ -64,78 +53,162 @@ def _in_appimage():
     return "APPIMAGE" in os.environ
 
 
-def apply_host_lua_paths(env):
-    """Prepend host Lua module dirs to LUA_PATH / LUA_CPATH (Flatpak only).
-
-    Must be called after user-defined lua_env overrides are applied, so host
-    paths are always first regardless of user config. User-defined paths remain
-    in the variable but after the host ones.
-    """
-    if not _in_flatpak():
-        return
-    _LUA_VERSIONS = ["5.5", "5.4", "5.3", "5.2", "5.1"]
-    _HOST = "/run/host/usr"
-    cpath_dirs, lpath_dirs = [], []
-    for v in _LUA_VERSIONS:
-        for base in [f"{_HOST}/lib/lua/{v}",
-                     f"{_HOST}/lib64/lua/{v}",
-                     f"{_HOST}/lib/x86_64-linux-gnu/lua/{v}"]:
-            cpath_dirs.append(f"{base}/?.so")
-        lpath_dirs.append(f"{_HOST}/share/lua/{v}/?.lua")
-        lpath_dirs.append(f"{_HOST}/share/lua/{v}/?/init.lua")
-    sep = ";"
-    host_cpath = sep.join(cpath_dirs)
-    host_lpath = sep.join(lpath_dirs)
-    # ;; keeps Lua's compiled-in defaults at the end as last resort
-    env["LUA_CPATH"] = host_cpath + sep + env.get("LUA_CPATH", ";;")
-    env["LUA_PATH"]  = host_lpath + sep + env.get("LUA_PATH",  ";;")
-
-
 def apply_host_libs(env):
-    """Prepare *env* for launching a host binary from inside our bundle.
+    """Strip bundle-local entries from *env* so a host binary can run cleanly.
 
-    - Flatpak: prepend host library dirs to LD_LIBRARY_PATH so the dynamic
-      linker can find host .so files mounted under /run/host.
-    - AppImage: strip $APPDIR-prefixed entries from LD_LIBRARY_PATH and
-      PYTHONPATH and drop PYTHONHOME, so the host interpreter doesn't try
-      to load the bundled (incompatible) Python lib/site-packages.
-    - Otherwise: no-op.
+    Only meaningful for AppImage: removes $APPDIR-prefixed entries from
+    LD_LIBRARY_PATH / PYTHONPATH / PATH and drops PYTHONHOME, so the host
+    interpreter doesn't try to load the bundled (incompatible) Python
+    lib/site-packages. Flatpak is handled via flatpak-spawn --host instead
+    (see flatpak_host_spawn), so the sandbox env is irrelevant there.
     """
-    if _in_flatpak():
-        dirs = ":".join(d for d in _FLATPAK_HOST_LIB_DIRS if os.path.isdir(d))
-        if dirs:
-            existing = env.get("LD_LIBRARY_PATH", "")
-            env["LD_LIBRARY_PATH"] = dirs + (":" + existing if existing else "")
+    if not _in_appimage():
         return
-    if _in_appimage():
-        appdir = os.environ.get("APPDIR", "")
-        if appdir:
-            for var, sep in (("LD_LIBRARY_PATH", ":"),
-                             ("PYTHONPATH", os.pathsep),
-                             ("PATH", os.pathsep)):
-                cur = env.get(var, "")
-                if not cur:
-                    continue
-                cleaned = sep.join(
-                    p for p in cur.split(sep)
-                    if p and not p.startswith(appdir)
-                )
-                if cleaned:
-                    env[var] = cleaned
-                else:
-                    env.pop(var, None)
-        env.pop("PYTHONHOME", None)
+    appdir = os.environ.get("APPDIR", "")
+    if appdir:
+        for var, sep in (("LD_LIBRARY_PATH", ":"),
+                         ("PYTHONPATH", os.pathsep),
+                         ("PATH", os.pathsep)):
+            cur = env.get(var, "")
+            if not cur:
+                continue
+            cleaned = sep.join(
+                p for p in cur.split(sep)
+                if p and not p.startswith(appdir)
+            )
+            if cleaned:
+                env[var] = cleaned
+            else:
+                env.pop(var, None)
+    env.pop("PYTHONHOME", None)
+
+
+# ---------- Flatpak: spawn on host outside the sandbox -----------------------
+#
+# Inside a Flatpak the sandbox glibc is incompatible with host shared libraries,
+# so we can't run host Python/Lua under the sandbox runtime — `LD_LIBRARY_PATH`
+# tricks hit a `_dl_call_libc_early_init` assertion. The supported way out is
+# `flatpak-spawn --host`, which talks to the session-bus Flatpak D-Bus service
+# (org.freedesktop.Flatpak.Development) and asks it to spawn a process in the
+# host execution environment instead of inside our sandbox. The manifest must
+# grant `--talk-name=org.freedesktop.Flatpak` for the D-Bus call to be allowed.
+#
+# The host process can't see our /app/ contents (sandbox-only), so when we
+# spawn host Python/Lua to run `py_func` / `lua_func`, the cwd must be a
+# directory both sides can reach. /tmp is shared (--filesystem=/tmp), so we
+# stage the testium package there once per process and reuse it for every
+# spawn. In source mode (testium under $HOME) the host already sees the
+# original path, so we skip the copy.
+
+_staged_testium_path = None
+
+
+def _get_host_testium_path():
+    """Return a path to the testium package that the host can read.
+
+    - Source / wheel / PyInstaller install under $HOME → return testium_path()
+      as-is (host sees the same path via --filesystem=home).
+    - Flatpak bundle (testium under /app/) → stage a copy under /tmp on first
+      call and reuse it for the rest of the process.
+    """
+    global _staged_testium_path
+    if _staged_testium_path is not None:
+        return _staged_testium_path
+
+    # Imported lazily to avoid a circular import (paths.py -> api.testium).
+    from interpreter.utils.paths import testium_path
+    tp = testium_path()
+
+    if not tp.startswith("/app/"):
+        _staged_testium_path = tp
+        return tp
+
+    staged = tempfile.mkdtemp(prefix="testium_host_", dir="/tmp")
+    # copytree refuses to write into an existing dir unless dirs_exist_ok=True.
+    # mkdtemp creates the dir, so we copy *into* it.
+    for entry in os.listdir(tp):
+        src = os.path.join(tp, entry)
+        dst = os.path.join(staged, entry)
+        if os.path.isdir(src):
+            shutil.copytree(src, dst, symlinks=True)
+        else:
+            shutil.copy2(src, dst, follow_symlinks=False)
+    _staged_testium_path = staged
+    atexit.register(shutil.rmtree, staged, ignore_errors=True)
+    return staged
+
+
+_FORWARDED_ENV_KEYS = (
+    "HOME", "USER", "LOGNAME", "TMPDIR",
+    "XDG_RUNTIME_DIR", "XDG_DATA_HOME", "XDG_CONFIG_HOME", "XDG_CACHE_HOME",
+    "DBUS_SESSION_BUS_ADDRESS", "DISPLAY", "WAYLAND_DISPLAY",
+    "LANG", "LC_ALL",
+)
+
+
+def flatpak_host_spawn(interp_bin, cmd_args, host_cwd, extra_env=None):
+    """Build a flatpak-spawn --host command vector.
+
+    Args:
+        interp_bin: absolute path to the host interpreter (e.g. /usr/bin/python3).
+        cmd_args: list of arguments passed to the interpreter.
+        host_cwd: working directory on the host (must be reachable from host).
+        extra_env: optional {name: value} of env vars to set on the host side
+                   in addition to the default forwarded set. Values of ""
+                   unset the variable on the host.
+
+    Returns a list suitable for subprocess.Popen.
+    """
+    spawn = ["flatpak-spawn", "--host", f"--directory={host_cwd}"]
+    forwarded = {}
+    for key in _FORWARDED_ENV_KEYS:
+        val = os.environ.get(key)
+        if val:
+            forwarded[key] = val
+    if extra_env:
+        forwarded.update(extra_env)
+    for k, v in forwarded.items():
+        if v == "":
+            spawn.append(f"--unset-env={k}")
+        else:
+            spawn.append(f"--env={k}={v}")
+    spawn.append(interp_bin)
+    spawn.extend(cmd_args)
+    return spawn
+
+
+def _which_host_flatpak(name):
+    """Resolve a binary name (or absolute path) on the host via flatpak-spawn.
+
+    We can't probe /run/host/... because (a) only host-os is mounted there,
+    not arbitrary paths like /scratch, and (b) returning a /run/host path
+    would be useless — the host-side spawn sees a different filesystem and
+    needs the host-native path anyway.
+    """
+    if os.path.isabs(name):
+        cmd = flatpak_host_spawn("/bin/sh", ["-c", f'test -x "{name}"'],
+                                 host_cwd="/tmp")
+        try:
+            r = subprocess.run(cmd, capture_output=True, timeout=10)
+        except (FileNotFoundError, PermissionError, subprocess.TimeoutExpired):
+            return ""
+        return name if r.returncode == 0 else ""
+    cmd = flatpak_host_spawn("/bin/sh", ["-c", f'command -v "{name}"'],
+                             host_cwd="/tmp")
+    try:
+        r = subprocess.run(cmd, capture_output=True, text=True, timeout=10)
+    except (FileNotFoundError, PermissionError, subprocess.TimeoutExpired):
+        return ""
+    if r.returncode != 0:
+        return ""
+    return r.stdout.strip()
 
 
 def _which(name):
     if tm.OS() == "Windows":
         return sys_app_path_win(name)
     if _in_flatpak():
-        for d in _FLATPAK_HOST_DIRS:
-            p = os.path.join(d, name)
-            if os.path.isfile(p) and os.access(p, os.X_OK):
-                return p
-        return ""
+        return _which_host_flatpak(name)
     if _in_appimage():
         for d in _APPIMAGE_HOST_DIRS:
             p = os.path.join(d, name)
@@ -146,14 +219,33 @@ def _which(name):
 
 
 def _probe_env():
-    """Subprocess env for probing host binaries (adds host libs in Flatpak)."""
+    """Subprocess env for probing host binaries.
+
+    In AppImage we still need to scrub APPDIR-prefixed entries; in Flatpak we
+    delegate execution to the host via flatpak-spawn so the sandbox env doesn't
+    matter, but apply_host_libs is a no-op cost.
+    """
     env = os.environ.copy()
     apply_host_libs(env)
     return env
 
 
-def _python_version(path):
-    cmd = [path, "-c", "import sys; print(sys.version_info[:3])"]
+def _run_probe(cmd):
+    """Run a probe command, dispatching through flatpak-spawn --host in Flatpak.
+
+    Returns (stdout, stderr) as str, or None on failure.
+    """
+    if _in_flatpak():
+        spawn = flatpak_host_spawn(cmd[0], cmd[1:], host_cwd="/tmp")
+        try:
+            r = subprocess.run(
+                spawn, capture_output=True, text=True, timeout=10,
+            )
+        except (FileNotFoundError, PermissionError, subprocess.TimeoutExpired):
+            return None
+        if r.returncode != 0:
+            return None
+        return r.stdout, r.stderr
     try:
         r = subprocess.run(
             cmd, capture_output=True, text=True,
@@ -161,8 +253,15 @@ def _python_version(path):
         )
     except (FileNotFoundError, PermissionError, subprocess.TimeoutExpired):
         return None
+    return r.stdout, r.stderr
+
+
+def _python_version(path):
+    out = _run_probe([path, "-c", "import sys; print(sys.version_info[:3])"])
+    if out is None:
+        return None
     try:
-        return eval(r.stdout)
+        return eval(out[0])
     except Exception:
         return None
 
@@ -173,15 +272,11 @@ def _is_python3(path):
 
 
 def _lua_version(path):
-    try:
-        r = subprocess.run(
-            [path, "-v"], capture_output=True, text=True, timeout=10,
-            env=_probe_env(),
-        )
-    except (FileNotFoundError, PermissionError, subprocess.TimeoutExpired):
+    out = _run_probe([path, "-v"])
+    if out is None:
         return None
     # On Windows the version banner goes to stderr.
-    line = r.stdout or r.stderr
+    line = out[0] or out[1]
     try:
         major, minor, _patch = line.split(" ")[1].split(".")
         return (int(major), int(minor))
@@ -202,22 +297,33 @@ _SPECS = {
     "lua":    ("Lua 5.1+",  "lua_bin",    _LUA_CANDIDATES,    _is_lua51),
 }
 
+# Cached per (name, override) so that runtime changes to gd[gd_key] —
+# e.g. ``python_bin`` set from a YAML config file loaded *after*
+# eval_proc has already resolved its own interpreter — are picked up by
+# the next lookup instead of returning the stale, auto-discovered path.
+# Long-lived subprocesses (eval_proc) keep whatever they captured at
+# construction time, but every new PyProcessBase / FuncExecEngine spawned
+# afterwards sees the current override.
 _resolved = {}
 
 
 def _resolve(name):
-    if name in _resolved:
-        return _resolved[name]
-
     display, gd_key, candidates, validator = _SPECS[name]
     override = tm.gd(gd_key, "") or ""
 
+    cached = _resolved.get(name)
+    if cached is not None and cached[0] == override:
+        return cached[1]
+
     path = ""
     if override:
         # Absolute path: accept as-is (user knows exactly what they want).
         # Bare name: resolve via _which() so the override stays host-only in
         # Flatpak/AppImage instead of silently picking the bundled interpreter.
-        if os.path.isabs(override):
+        # In Flatpak we always defer to _which() so even absolute paths are
+        # checked from the host's perspective (the sandbox can't see e.g.
+        # /scratch/... paths that the user may have configured).
+        if os.path.isabs(override) and not _in_flatpak():
             resolved = override if (os.path.isfile(override)
                                     and os.access(override, os.X_OK)) else ""
         else:
@@ -239,7 +345,7 @@ def _resolve(name):
                 path = p
                 break
 
-    _resolved[name] = path
+    _resolved[name] = (override, path)
     return path
 
 

src/testium/interpreter/utils/lua_process.py

@@ -47,9 +47,16 @@ class LuaProcessBase:
         if self._process is not None:
             raise ETUMRuntimeError("The function subprocess has already been started.")
 
-        func_proc_path = os.path.realpath(
-            os.path.join(subproc_path(), "lua_func")
-        )
+        # In Flatpak the host can't see /app/lib/testium/lua_func, so use a
+        # staged copy under /tmp (shared between sandbox and host).
+        if bins._in_flatpak():
+            func_proc_path = os.path.join(
+                bins._get_host_testium_path(), "lua_func"
+            )
+        else:
+            func_proc_path = os.path.realpath(
+                os.path.join(subproc_path(), "lua_func")
+            )
 
         # POpen config
         CUST_ENV = {
@@ -71,7 +78,6 @@ class LuaProcessBase:
                     env[k] = e
                 else:
                     env[k] = e + ";" + env.get(k, "")
-        bins.apply_host_lua_paths(env)
 
         sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
         sock.bind(("localhost", 0))
@@ -79,8 +85,7 @@ class LuaProcessBase:
         sock.close()
 
         # POpen params
-        params = [
-            self._lbin,
+        cmd_args = [
             "main.lua",
             "--timeout",
             f"{self._timeout}",
@@ -91,14 +96,31 @@ class LuaProcessBase:
         ]
 
         if tm.debug_enabled() and tm.gd("debug_rpc", False):
-            params.append("--verbose")
+            cmd_args.append("--verbose")
+
+        if bins._in_flatpak():
+            # Run on the host outside the sandbox: avoids glibc ABI mismatches
+            # between the Flatpak runtime and host shared libraries.
+            host_env = {
+                k: env[k] for k in ("LUA_PATH", "LUA_CPATH", "PATH")
+                if k in env and env[k]
+            }
+            params = bins.flatpak_host_spawn(
+                self._lbin, cmd_args, host_cwd=func_proc_path,
+                extra_env=host_env,
+            )
+            popen_kwargs = {}
+        else:
+            params = [self._lbin, *cmd_args]
+            popen_kwargs = {"env": env, "cwd": func_proc_path}
 
         self._process = subprocess.Popen(
-            params, env=env, cwd=func_proc_path,
+            params,
             stdin=subprocess.DEVNULL,
             stdout=subprocess.PIPE,
             stderr=subprocess.PIPE,
             restore_signals=False,
+            **popen_kwargs,
         )
         # Route subprocess stdout/stderr (lua require failures, syntax
         # errors, anything written to fd 1/2 before the in-script

src/testium/interpreter/utils/py_process.py

@@ -61,14 +61,18 @@ class PyProcessBase:
         if sock is not None:
             sock.close()
 
-        # Add the path of the subprocess (root sources of testium)
-        tstium_path = os.path.realpath(testium_path())
-        func_proc_path = os.path.realpath(subproc_path())
+        # In Flatpak the host can't see /app/lib/testium, so use a staged copy
+        # under /tmp (shared between sandbox and host) for both cwd and as the
+        # root in PYTHONPATH. Outside Flatpak the original paths are used.
+        if bins._in_flatpak():
+            tstium_path = bins._get_host_testium_path()
+            func_proc_path = tstium_path
+        else:
+            tstium_path = os.path.realpath(testium_path())
+            func_proc_path = os.path.realpath(subproc_path())
         env["PYTHONPATH"] = tstium_path + os.pathsep + self._ppath + os.pathsep + env.get("PYTHONPATH", "")
 
-        params = [
-            self._pbin,
-            # "-m",
+        cmd_args = [
             "py_func",
             "-p",
             f"{self._port}",
@@ -77,14 +81,31 @@ class PyProcessBase:
         ]
 
         if tm.debug_enabled() and tm.gd("debug_rpc", False):
-            params.append("-v")
+            cmd_args.append("-v")
+
+        if bins._in_flatpak():
+            # Run on the host outside the sandbox: avoids glibc ABI mismatches
+            # between the Flatpak runtime and host shared libraries.
+            host_env = {
+                k: env[k] for k in ("PYTHONPATH", "PATH")
+                if k in env and env[k]
+            }
+            params = bins.flatpak_host_spawn(
+                self._pbin, cmd_args, host_cwd=func_proc_path,
+                extra_env=host_env,
+            )
+            popen_kwargs = {}
+        else:
+            params = [self._pbin, *cmd_args]
+            popen_kwargs = {"env": env, "cwd": func_proc_path}
 
         self._process = subprocess.Popen(
-            params, env=env, cwd=func_proc_path,
+            params,
             stdin=subprocess.DEVNULL,
             stdout=subprocess.PIPE,
             stderr=subprocess.PIPE,
             restore_signals=False,
+            **popen_kwargs,
         )
         # Route subprocess stdout/stderr (early-startup errors,
         # unhandled exceptions, anything written to fd 1/2 before the

src/testium/interpreter/utils/test_init.py

@@ -165,11 +165,14 @@ def env_init():
     _constants_init()
 
 
-def update_global(config_files, defines, gui_defaults, silent=False):
-    """Global dict updated with the content of the config file and a dict provided.
-    this function returns the resulting dict.
+def apply_overrides(defines, gui_defaults):
+    """Push GUI defaults then CLI defines into the global dict.
+
+    Extracted from update_global so it can be called *before* eval_proc
+    starts: interpreter overrides (python_bin, lua_bin) must be visible
+    to bins.python_bin() on its first lookup, which happens during
+    eval_process_init.
     """
-    # GUI preferences applied first
     for k, v in gui_defaults.items():
         try:
             val = ast.literal_eval(v)
@@ -177,7 +180,6 @@ def update_global(config_files, defines, gui_defaults, silent=False):
             val = v
         tm.setgd(k, val)
 
-    # Then command line defines
     for k, v in defines.items():
         try:
             val = ast.literal_eval(v)
@@ -185,6 +187,14 @@ def update_global(config_files, defines, gui_defaults, silent=False):
             val = v
         tm.setgd(k, val)
 
+
+def update_global(config_files, defines, gui_defaults, silent=False):
+    """Global dict updated with the content of the config file and a dict provided.
+    this function returns the resulting dict.
+    """
+    # GUI preferences applied first, then command line defines
+    apply_overrides(defines, gui_defaults)
+
     # Then the configuration files
     # load global dic before test item
     _feed_gd_with_params(config_files, silent)

src/testium/lua_func/json-rpc.lua

@@ -41,8 +41,7 @@ end
 --- INTERNAL: Handle requests from the client
 function JSONRPC:_handle_request(req)
     local method = self.methods[req.method]
-    local ok, ret
-    local res, err
+    local ok, ret, err
     if not method then
         if req.id then self:_send_error(req.id, string.format("Method '%s' not registered in lua server")) end
         return
@@ -52,15 +51,18 @@ function JSONRPC:_handle_request(req)
 
     -- Only send response if it's not a Notification (notifications have no ID)
     if req.id then
-        if ok then
-            res = ret
-            if res == nil then
-                self:_send_error(req.id, tostring(err))
-            else
-                self:_send({ jsonrpc = "2.0", result = { returned_value = res }, id = req.id })
-            end
-        else
+        if not ok then
+            -- pcall trapped a runtime error in the method itself.
+            self:_send_error(req.id, tostring(ret))
+        elseif err ~= nil then
+            -- Method ran but signaled a logical error via its 2nd return.
             self:_send_error(req.id, tostring(err))
+        else
+            -- Success. A user function returning nothing yields ret==nil;
+            -- encode it as JSON null so "returned_value" stays present.
+            local val = ret
+            if val == nil then val = json.null end
+            self:_send({ jsonrpc = "2.0", result = { returned_value = val }, id = req.id })
         end
     end
 end

src/testium/main_win/file_dialog.py

@@ -0,0 +1,21 @@
+"""Helpers for Qt file/directory dialogs.
+
+In Flatpak the native QFileDialog goes through the XDG document portal,
+which returns ``/run/user/UID/doc/.../<file>`` and only exposes the
+selected file — sibling files (param.yaml, scripts, recent paths in
+preferences, ...) are unreachable. Forcing Qt's own non-native dialog
+makes it walk the real filesystem mounted via ``--filesystem=home``
+and return a regular path.
+"""
+
+import os
+
+from PySide6.QtWidgets import QFileDialog
+
+
+def options():
+    """Default ``QFileDialog`` options for the current runtime."""
+    opts = QFileDialog.Options()
+    if os.path.isfile("/.flatpak-info"):
+        opts |= QFileDialog.Option.DontUseNativeDialog
+    return opts

src/testium/main_win/preference_win/preference_win.py

@@ -3,6 +3,7 @@ from PySide6.QtWidgets import QDialog, QFileDialog
 from PySide6.QtGui import QFont
 
 from main_win.preference_win.preference_core_win import Ui_preferenceWindow
+from main_win import file_dialog
 
 import interpreter.utils.settings as prefs
 
@@ -193,6 +194,7 @@ class PrefWindow(QDialog):
             self,
             caption="Select the default report directory",
             dir=self.ui.editDefaultReportPath.text(),
+            options=file_dialog.options(),
         )
         if path:
             self.ui.editDefaultReportPath.setText(path)
@@ -203,6 +205,7 @@ class PrefWindow(QDialog):
             self,
             caption="Select the default log directory",
             dir=self.ui.editDefaultLogPath.text(),
+            options=file_dialog.options(),
         )
         if path:
             self.ui.editDefaultLogPath.setText(path)
@@ -213,6 +216,7 @@ class PrefWindow(QDialog):
             self,
             caption="Select the python interpreter",
             dir=self.ui.editPythonPath.text(),
+            options=file_dialog.options(),
         )
         if path:
             self.ui.editPythonPath.setText(path)
@@ -220,7 +224,10 @@ class PrefWindow(QDialog):
     @Slot()
     def on_butLuaPath_pressed(self):
         path, _ = QFileDialog.getOpenFileName(
-            self, caption="Select the lua interpreter", dir=self.ui.editLuaPath.text()
+            self,
+            caption="Select the lua interpreter",
+            dir=self.ui.editLuaPath.text(),
+            options=file_dialog.options(),
         )
         if path:
             self.ui.editLuaPath.setText(path)

src/testium/main_win/test_file_manager.py

@@ -9,6 +9,7 @@ from PySide6.QtWidgets import QApplication, QFileDialog, QProgressDialog
 from interpreter.process import TestProcess
 from interpreter.utils.test_ctrl import TestSetController
 from main_win.test_controller_service import TestControllerService
+from main_win import file_dialog
 import interpreter.utils.settings as prefs
 from runtime.tum_except import ETUMFileError, ETUMRuntimeError
 
@@ -212,17 +213,9 @@ class TestFileManager:
         d = ""
         if w.testFile is not None:
             d = os.path.dirname(w.testFile)
-        # In Flatpak the native dialog goes through the XDG document portal,
-        # which returns /run/user/UID/doc/.../test.tum and only exposes the
-        # selected file — sibling files (param.yaml, .py, etc.) are unreachable.
-        # Force Qt's own dialog, which walks the real filesystem mounted via
-        # --filesystem=home and returns a regular path with sibling access.
-        options = QFileDialog.Options()
-        if os.path.isfile("/.flatpak-info"):
-            options |= QFileDialog.Option.DontUseNativeDialog
         file_name, _ = QFileDialog.getOpenFileName(
             w, "Open the test file", d,
-            "testium file (*.tum);;All Files (*)", options=options
+            "testium file (*.tum);;All Files (*)", options=file_dialog.options()
         )
         if file_name:
             self.reload(file_name)

src/testium/main_win/testium_win.py

@@ -37,6 +37,7 @@ from interpreter.utils.icons import icon_prefix
 
 from main_win.test_run.outlog import OutLog
 from main_win.test_run.test_run import ThreadTestStatus
+from main_win import file_dialog
 import interpreter.utils.settings as prefs
 from runtime.stdout_redirect import stdio_redir
 import api.testium as tm
@@ -484,7 +485,8 @@ class MainWindow(QMainWindow, Ui_MainWindow):
         else:
             initialPath = None
         fileName, _ = QFileDialog.getSaveFileName(
-            self, "Path to Log file", initialPath, "Log Files (*.log);;All Files (*)"
+            self, "Path to Log file", initialPath, "Log Files (*.log);;All Files (*)",
+            options=file_dialog.options(),
         )
         if fileName:
             shutil.copy(self.logFileName, fileName)
@@ -525,7 +527,8 @@ class MainWindow(QMainWindow, Ui_MainWindow):
         else:
             initialPath = None
         fileName, _ = QFileDialog.getSaveFileName(
-            self, "Path to log file", initialPath, "Log Files (*.log);;All Files (*)"
+            self, "Path to log file", initialPath, "Log Files (*.log);;All Files (*)",
+            options=file_dialog.options(),
         )
         if fileName:
             self.editLogFilePath.setText(fileName)

test/validation/README.md

@@ -1,10 +1,76 @@
 # Validation
 
-This directory contains the necessary material to run the testium validation.
+This directory contains the testium validation suite. A single set of
+items (`items/`), fixtures and post-processing (`post_execution.py`) is
+re-used across every packaging channel.
 
-Here is the documentation on how to configure the validation, run it and check that the
-results are correct.
+## Running the suite
 
-# Tests
+```sh
+./test/validation/run.sh                       # default mode = source
+./test/validation/run.sh --mode wheel
+./test/validation/run.sh --mode pyinstaller
+./test/validation/run.sh --mode flatpak
+./test/validation/run.sh --mode appimage
+```
 
-TBD
+On Windows (only `source`, `wheel`, `pyinstaller` are supported):
+
+```bat
+test\validation\run.bat --mode pyinstaller
+```
+
+Pass `clean` as the **first** argument to recreate the validation venv
+from scratch (useful after a system Python upgrade):
+
+```sh
+./test/validation/run.sh clean --mode flatpak
+```
+
+Any extra arguments after the mode flag are forwarded to testium.
+
+## Modes
+
+| Mode          | What it launches                                            | Prerequisite                                                     |
+|---------------|-------------------------------------------------------------|------------------------------------------------------------------|
+| `source`      | `python3 src/testium` via the project's `run.sh`            | none — works straight out of the repo                            |
+| `wheel`       | `python -m testium` inside a dedicated wheel venv           | `./build_all.sh` produced `dist/testium-<v>-py3-none-any.whl`    |
+| `pyinstaller` | `dist/testium-<v>` (frozen binary)                          | `./build_all.sh` produced the PyInstaller binary                 |
+| `flatpak`     | `flatpak run --command=testium org.testium.Testium`         | the Flatpak bundle is installed (`flatpak install --user dist/testium-<v>.flatpak`) |
+| `appimage`    | `dist/Testium-<v>-x86_64.AppImage`                          | `./build_all.sh` produced the AppImage                           |
+
+Each mode writes its results to a distinct report file
+(`validation-<mode>.sqlite` / `validation-<mode>-<item>.xml`), so you
+can run several modes in a row without clobbering previous reports.
+
+## How `python_bin` is pinned
+
+Every test-execution subprocess (inline `<| ... |>` evaluation,
+`py_func`, `cycle`, `post_execution`, …) is routed through a dedicated
+venv at `${TMPDIR:-/tmp}/testium-validation-venv`. The venv is created
+with `--system-site-packages` so existing system packages stay visible,
+then `junit-xml` is pip-installed for `post_execution.py`.
+
+This is a **host** venv. In every mode (including Flatpak) the
+test-execution subprocesses end up running on the host — directly for
+source/wheel/pyinstaller/appimage, and via `flatpak-spawn --host` for
+Flatpak — so the same venv works across modes. The wheel mode
+additionally creates a separate `testium-wheel-venv-<v>` to hold the
+installed wheel; that one is only used to launch testium itself.
+
+## What is checked
+
+The `venv` item under `items/venv/` asserts that the validation venv is
+actually being used:
+
+* `python_bin` is set in the global dict.
+* The eval subprocess (used for `<| ... |>` expressions) has
+  `sys.executable == python_bin`, `sys.prefix == dirname(dirname(python_bin))`,
+  and `sys.prefix != sys.base_prefix` (i.e. is actually inside a venv).
+* A `py_func` subprocess passes the same three checks.
+
+These checks use `abspath`/`normpath` rather than `realpath` on
+purpose: the venv's `bin/python3` is a symlink to the host interpreter,
+so `realpath` would map both venv and non-venv interpreters to the same
+target. `sys.prefix != sys.base_prefix` is the venv-specific marker
+that distinguishes the two cases.

test/validation/items/lua_func/lua_func.lua

@@ -49,4 +49,12 @@ function module.test_delgd()
     return 0
 end
 
+function module.return_nothing()
+    -- Returns no value: ret is nil but no error.
+end
+
+function module.return_explicit_nil()
+    return nil
+end
+
 return module

test/validation/items/lua_func/test.tum

@@ -186,6 +186,18 @@
     file: $(test_path)$(psep)lua_func.lua
     func_name: test_delgd
 
+- lua_func:
+    name: function returning nothing should succeed
+    key: $(test)_PASS
+    file: $(test_path)$(psep)lua_func.lua
+    func_name: return_nothing
+
+- lua_func:
+    name: function returning explicit nil should succeed
+    key: $(test)_PASS
+    file: $(test_path)$(psep)lua_func.lua
+    func_name: return_explicit_nil
+
 - group:
     name: context_id tests
     steps:

test/validation/items/py_func/py_func.py

@@ -54,3 +54,10 @@ def test_delgd():
     tm.delgd("_py_delgd_test")
     assert tm.gd("_py_delgd_test", None) is None
     return 0
+
+def return_nothing():
+    # Falls off the end: implicit None return, no error.
+    pass
+
+def return_explicit_none():
+    return None

test/validation/items/py_func/test.tum

@@ -196,6 +196,18 @@
     file: $(test_path)$(psep)py_func.py
     func_name: test_delgd
 
+- py_func:
+    name: function returning nothing should succeed
+    key: $(test)_PASS
+    file: $(test_path)$(psep)py_func.py
+    func_name: return_nothing
+
+- py_func:
+    name: function returning explicit None should succeed
+    key: $(test)_PASS
+    file: $(test_path)$(psep)py_func.py
+    func_name: return_explicit_none
+
 - group:
     name: context_id tests
     steps:

test/validation/items/venv/param.yaml

@@ -0,0 +1 @@
+no_param: Null

test/validation/items/venv/test.tum

@@ -0,0 +1,53 @@
+# venv test: assert that the dedicated validation venv is the python
+# being used for every test-execution subprocess (eval_proc / py_func /
+# cycle / ...). The venv path is pinned by ``-d python_bin=...`` in
+# test/validation/run.sh (or run.bat).
+#
+# We use ``abspath``/``normpath`` rather than ``realpath`` on purpose:
+# the venv's ``bin/python3`` is a symlink to the host python, so
+# realpath would map every venv interpreter to the same system path and
+# the comparison would silently pass even *without* a venv.
+# ``sys.prefix != sys.base_prefix`` is the venv-specific marker that
+# catches that case.
+
+- check:
+    name: python_bin is set in the global dict
+    key: $(test)_PASS
+    values:
+        - <| bool(r"$(python_bin)") |>
+
+- check:
+    name: eval_proc subprocess runs in the validation venv
+    key: $(test)_PASS
+    values:
+        - <| os.path.normpath(os.path.abspath(sys.executable)) == os.path.normpath(os.path.abspath(r"$(python_bin)")) |>
+
+- check:
+    name: eval_proc sys.prefix matches python_bin venv root
+    key: $(test)_PASS
+    values:
+        - <| os.path.normpath(os.path.abspath(sys.prefix)) == os.path.dirname(os.path.dirname(os.path.normpath(os.path.abspath(r"$(python_bin)")))) |>
+
+- check:
+    name: eval_proc is actually inside a venv (sys.prefix != sys.base_prefix)
+    key: $(test)_PASS
+    values:
+        - <| os.path.normpath(os.path.abspath(sys.prefix)) != os.path.normpath(os.path.abspath(sys.base_prefix)) |>
+
+- py_func:
+    name: py_func subprocess runs in the validation venv
+    key: $(test)_PASS
+    file: $(test_path)$(psep)verify_venv.py
+    func_name: check_sys_executable
+
+- py_func:
+    name: py_func sys.prefix matches python_bin venv root
+    key: $(test)_PASS
+    file: $(test_path)$(psep)verify_venv.py
+    func_name: check_sys_prefix_in_venv
+
+- py_func:
+    name: py_func is actually inside a venv
+    key: $(test)_PASS
+    file: $(test_path)$(psep)verify_venv.py
+    func_name: check_is_venv

test/validation/items/venv/verify_venv.py

@@ -0,0 +1,62 @@
+import os
+import sys
+
+import py_func.tm as tm
+
+
+def _norm(p):
+    # normpath + normcase, without resolving symlinks. realpath() would
+    # follow the venv's ``python3`` symlink to ``/usr/bin/python3.X`` and
+    # defeat the comparison.
+    return os.path.normcase(os.path.normpath(os.path.abspath(p)))
+
+
+def _venv_dir():
+    # python_bin is at ``<venv>/(bin|Scripts)/python*`` so the venv root
+    # is two levels above the executable.
+    exe = tm.gd("python_bin", "")
+    if not exe:
+        return ""
+    return os.path.dirname(os.path.dirname(_norm(exe)))
+
+
+def check_sys_executable():
+    """py_func subprocess: sys.executable must match the configured python_bin."""
+    expected = _norm(tm.gd("python_bin", ""))
+    actual = _norm(sys.executable)
+    if expected and actual == expected:
+        return True
+    return (
+        -1,
+        f"sys.executable={actual!r} differs from python_bin={expected!r}",
+    )
+
+
+def check_sys_prefix_in_venv():
+    """py_func subprocess: sys.prefix must match the venv root derived
+    from python_bin (two levels up from the executable)."""
+    venv = _venv_dir()
+    if not venv:
+        return (-1, "python_bin is not set in the global dict")
+    actual = _norm(sys.prefix)
+    if actual == venv:
+        return True
+    return (
+        -1,
+        f"sys.prefix={actual!r} is not the validation venv {venv!r}",
+    )
+
+
+def check_is_venv():
+    """py_func subprocess: confirm we are inside a venv, i.e. sys.prefix
+    differs from sys.base_prefix. This catches the case where python_bin
+    happens to be a system interpreter and the path-based check would
+    pass trivially."""
+    actual = _norm(sys.prefix)
+    base = _norm(sys.base_prefix)
+    if actual != base:
+        return True
+    return (
+        -1,
+        f"sys.prefix == sys.base_prefix == {actual!r}: not running in a venv",
+    )

test/validation/run.bat

@@ -0,0 +1,131 @@
+@echo off
+SETLOCAL EnableExtensions EnableDelayedExpansion
+
+REM Runs the testium validation suite against any installable channel of
+REM testium on Windows (source, wheel, pyinstaller).
+REM
+REM Usage:
+REM   test\validation\run.bat [clean] [--mode MODE] [extra testium args]
+REM
+REM   clean       remove the validation venv before recreating it
+REM               (must be the first argument; useful after a Python upgrade)
+REM
+REM   --mode MODE which testium build to validate. One of:
+REM                   source       (default) project's run.bat (src\testium)
+REM                   wheel        dist\testium-<v>-py3-none-any.whl
+REM                   pyinstaller  dist\testium-<v>.exe (or dist\testium-<v>)
+REM
+REM Every test-execution subprocess runs in a dedicated host venv under
+REM %TEMP%\testium-validation-venv (created with --system-site-packages,
+REM then junit-xml is pip-installed for post_execution.py).
+REM
+REM The report file is suffixed with the mode so consecutive runs in
+REM different modes don't overwrite each other.
+
+SET "SCRIPT_DIR=%~dp0"
+IF "%SCRIPT_DIR:~-1%"=="\" SET "SCRIPT_DIR=%SCRIPT_DIR:~0,-1%"
+SET "PROJECT_DIR=%SCRIPT_DIR%\..\.."
+SET /P VERSION=<"%PROJECT_DIR%\src\VERSION"
+
+REM ---------- arg parsing ----------------------------------------------------
+
+SET "MODE=source"
+SET "CLEAN=0"
+IF /I "%~1"=="clean" (
+    SET "CLEAN=1"
+    SHIFT
+)
+
+SET "EXTRA="
+:PARSE_ARGS
+IF "%~1"=="" GOTO ARGS_DONE
+IF /I "%~1"=="--mode" (
+    SET "MODE=%~2"
+    SHIFT
+    SHIFT
+    GOTO PARSE_ARGS
+)
+SET "EXTRA=!EXTRA! "%~1""
+SHIFT
+GOTO PARSE_ARGS
+:ARGS_DONE
+
+REM ---------- locate host python ---------------------------------------------
+
+SET "PYTHON_EXE="
+py --version >nul 2>&1
+IF %ERRORLEVEL% EQU 0 (
+    SET "PYTHON_EXE=py"
+    GOTO PYTHON_FOUND
+)
+python --version >nul 2>&1
+IF %ERRORLEVEL% EQU 0 (
+    SET "PYTHON_EXE=python"
+    GOTO PYTHON_FOUND
+)
+echo ERROR: Python could not be found on this system.
+exit /b 1
+:PYTHON_FOUND
+
+REM ---------- validation venv -------------------------------------------------
+
+SET "VENV_DIR=%TEMP%\testium-validation-venv"
+IF "%CLEAN%"=="1" IF EXIST "%VENV_DIR%" rmdir /s /q "%VENV_DIR%"
+
+IF NOT EXIST "%VENV_DIR%" (
+    echo Creating validation venv at %VENV_DIR%
+    %PYTHON_EXE% -m venv --system-site-packages "%VENV_DIR%"
+    IF !ERRORLEVEL! NEQ 0 (
+        echo ERROR while creating the validation venv.
+        exit /b 1
+    )
+    call "%VENV_DIR%\Scripts\pip" install --quiet --upgrade pip
+    call "%VENV_DIR%\Scripts\pip" install --quiet junit-xml
+)
+SET "VENV_PYTHON=%VENV_DIR%\Scripts\python.exe"
+
+REM ---------- shared "tail" forwarded to every launcher -----------------------
+REM Reports are stamped with the mode so successive runs don't clobber each other.
+
+SET "TAIL=-b -d "python_bin=%VENV_PYTHON%" -d "validation_report_file=validation-%MODE%" -- "%SCRIPT_DIR%\main.tum"%EXTRA%"
+
+REM ---------- per-mode launcher ----------------------------------------------
+
+echo -- validation mode: %MODE%
+
+IF /I "%MODE%"=="source"      GOTO MODE_SOURCE
+IF /I "%MODE%"=="wheel"       GOTO MODE_WHEEL
+IF /I "%MODE%"=="pyinstaller" GOTO MODE_PYI
+echo ERROR: unknown --mode '%MODE%'. Expected: source ^| wheel ^| pyinstaller.
+exit /b 1
+
+:MODE_SOURCE
+call "%PROJECT_DIR%\run.bat" %TAIL%
+exit /b %ERRORLEVEL%
+
+:MODE_WHEEL
+SET "WHEEL=%PROJECT_DIR%\dist\testium-%VERSION%-py3-none-any.whl"
+IF NOT EXIST "%WHEEL%" (
+    echo ERROR: wheel not found at %WHEEL% -- run build_all.sh first.
+    exit /b 1
+)
+SET "WHEEL_VENV=%TEMP%\testium-wheel-venv-%VERSION%"
+IF "%CLEAN%"=="1" IF EXIST "%WHEEL_VENV%" rmdir /s /q "%WHEEL_VENV%"
+IF NOT EXIST "%WHEEL_VENV%" (
+    echo Creating wheel venv at %WHEEL_VENV%
+    %PYTHON_EXE% -m venv --system-site-packages "%WHEEL_VENV%"
+    call "%WHEEL_VENV%\Scripts\pip" install --quiet --upgrade pip
+    call "%WHEEL_VENV%\Scripts\pip" install --quiet "%WHEEL%"
+)
+"%WHEEL_VENV%\Scripts\python.exe" -m testium %TAIL%
+exit /b %ERRORLEVEL%
+
+:MODE_PYI
+SET "PYI_BIN=%PROJECT_DIR%\dist\testium-%VERSION%.exe"
+IF NOT EXIST "%PYI_BIN%" SET "PYI_BIN=%PROJECT_DIR%\dist\testium-%VERSION%"
+IF NOT EXIST "%PYI_BIN%" (
+    echo ERROR: PyInstaller binary not found in %PROJECT_DIR%\dist -- run build_all.sh first.
+    exit /b 1
+)
+"%PYI_BIN%" %TAIL%
+exit /b %ERRORLEVEL%

test/validation/run.sh

@@ -0,0 +1,143 @@
+#!/bin/bash
+# Runs the testium validation suite against any installable channel of
+# testium (source, wheel, pyinstaller, flatpak, appimage).
+#
+# Usage:
+#   ./test/validation/run.sh [clean] [--mode MODE] [extra testium args]
+#
+#   clean           remove the validation venv before recreating it
+#                   (must be the first argument; useful after a Python upgrade)
+#
+#   --mode MODE     which testium build to validate. One of:
+#                       source       (default) src/testium via project run.sh
+#                       wheel        dist/testium-<v>-py3-none-any.whl
+#                       pyinstaller  dist/testium-<v>
+#                       flatpak      installed org.testium.Testium
+#                       appimage     dist/Testium-<v>-*.AppImage
+#
+# Every test-execution subprocess (inline <| ... |>, py_func, cycle,
+# post_execution, ...) runs in a dedicated host venv under
+# /tmp/testium-validation-venv. That venv is shared across modes —
+# even Flatpak reaches it via flatpak-spawn --host. The validation venv
+# is created with --system-site-packages so existing system packages
+# (PySide6, lxml, ...) stay visible, then junit-xml is pip-installed
+# for post_execution.py.
+#
+# The report file is suffixed with the mode (e.g. validation-flatpak.sqlite)
+# so consecutive runs in different modes don't overwrite each other.
+
+set -e
+
+SCRIPT_PATH="$(readlink -f "$0")"
+SCRIPT_DIR="$(realpath "$(dirname "$SCRIPT_PATH")")"
+PROJECT_DIR="$(realpath "$SCRIPT_DIR/../..")"
+VERSION="$(cat "$PROJECT_DIR/src/VERSION")"
+
+# ---------- arg parsing -------------------------------------------------------
+
+MODE=source
+
+if [ "${1:-}" = "clean" ]; then
+    CLEAN=1
+    shift
+else
+    CLEAN=0
+fi
+
+EXTRA=()
+while [ $# -gt 0 ]; do
+    case "$1" in
+        --mode)
+            MODE="$2"
+            shift 2
+            ;;
+        --mode=*)
+            MODE="${1#--mode=}"
+            shift
+            ;;
+        *)
+            EXTRA+=("$1")
+            shift
+            ;;
+    esac
+done
+
+# ---------- validation venv ---------------------------------------------------
+
+VENV_DIR="${TMPDIR:-/tmp}/testium-validation-venv"
+if [ "$CLEAN" -eq 1 ]; then
+    rm -rf "$VENV_DIR"
+fi
+
+if [ ! -d "$VENV_DIR" ]; then
+    echo "Creating validation venv at $VENV_DIR"
+    python3 -m venv --system-site-packages "$VENV_DIR"
+    "$VENV_DIR/bin/pip" install --quiet --upgrade pip
+    "$VENV_DIR/bin/pip" install --quiet junit-xml
+fi
+VENV_PYTHON="$VENV_DIR/bin/python3"
+
+# ---------- per-mode launcher -------------------------------------------------
+
+case "$MODE" in
+    source)
+        CMD=("$PROJECT_DIR/run.sh")
+        ;;
+    wheel)
+        WHEEL="$PROJECT_DIR/dist/testium-${VERSION}-py3-none-any.whl"
+        if [ ! -f "$WHEEL" ]; then
+            echo "ERROR: wheel not found at $WHEEL — run ./build_all.sh first." >&2
+            exit 1
+        fi
+        WHEEL_VENV="${TMPDIR:-/tmp}/testium-wheel-venv-${VERSION}"
+        if [ "$CLEAN" -eq 1 ]; then
+            rm -rf "$WHEEL_VENV"
+        fi
+        if [ ! -d "$WHEEL_VENV" ]; then
+            echo "Creating wheel venv at $WHEEL_VENV"
+            python3 -m venv --system-site-packages "$WHEEL_VENV"
+            "$WHEEL_VENV/bin/pip" install --quiet --upgrade pip
+            "$WHEEL_VENV/bin/pip" install --quiet "$WHEEL"
+        fi
+        CMD=("$WHEEL_VENV/bin/python" -m testium)
+        ;;
+    pyinstaller)
+        PYI_BIN="$PROJECT_DIR/dist/testium-${VERSION}"
+        if [ ! -x "$PYI_BIN" ]; then
+            echo "ERROR: PyInstaller binary not found at $PYI_BIN — run ./build_all.sh first." >&2
+            exit 1
+        fi
+        CMD=("$PYI_BIN")
+        ;;
+    flatpak)
+        if ! flatpak info --user org.testium.Testium &>/dev/null \
+           && ! flatpak info --system org.testium.Testium &>/dev/null; then
+            echo "ERROR: org.testium.Testium is not installed." >&2
+            echo "       flatpak install --user $PROJECT_DIR/dist/testium-${VERSION}.flatpak" >&2
+            exit 1
+        fi
+        CMD=(flatpak run --command=testium org.testium.Testium)
+        ;;
+    appimage)
+        APPIMAGE=$(ls -1t "$PROJECT_DIR/dist"/Testium-"${VERSION}"-*.AppImage 2>/dev/null | head -1)
+        if [ -z "$APPIMAGE" ] || [ ! -x "$APPIMAGE" ]; then
+            echo "ERROR: no AppImage for version $VERSION under $PROJECT_DIR/dist — run ./build_all.sh first." >&2
+            exit 1
+        fi
+        CMD=("$APPIMAGE")
+        ;;
+    *)
+        echo "ERROR: unknown --mode '$MODE'. Expected: source|wheel|pyinstaller|flatpak|appimage." >&2
+        exit 1
+        ;;
+esac
+
+# ---------- launch ------------------------------------------------------------
+
+echo "-- validation mode: $MODE"
+echo "-- launch: ${CMD[*]}"
+
+exec "${CMD[@]}" -b \
+    -d "python_bin=$VENV_PYTHON" \
+    -d "validation_report_file=validation-$MODE" \
+    -- "$SCRIPT_DIR/main.tum" "${EXTRA[@]}"