M9.R.38.3: skip nix-store Qt6 dirs in launcher Qt plugin/QML walk

ROOT CAUSE (G2 install ``munmap_chunk(): invalid pointer`` SIGABRT
before Phase 1):

The reproos-installer-launcher.sh walks ``/nix/store/*/lib`` and
adds every dir containing ``qt-6/plugins`` to QT_PLUGIN_PATH +
QT_QPA_PLATFORM_PLUGIN_PATH, every dir containing ``qt-6/qml`` to
QML2_IMPORT_PATH.  The de-rootfs nix-store mirror ships:

  /nix/store/zp6r9bxds...-qtbase-6.10.1/lib/qt-6/plugins/

pulled in as a transitive of layer-shell-qt-6.5.3 (in the DE
closure).  But the installer is COMPILED + RPATH'd against:

  /opt/repro/.../qt6-base/.repro/output/install/usr/lib/  (Qt 6.8.1)

When Qt 6.8.1 binary loads a Qt 6.10.1 ``libqoffscreen.so`` plugin
under QT_QPA_PLATFORM=offscreen, the C++ ABI mismatch corrupts the
heap during plugin init and glibc's ``munmap_chunk()`` detects the
bad pointer + raises SIGABRT.

WHY M9.R.37 DIDN'T HIT THIS:

The M9.R.37 18:47 install used the installer binary built at 21:28
(this was before MY 00:11 rebuild that this commit unblocks).  At
the M9.R.37 build time the de-rootfs nix-store mirror layout may
have been different -- the Qt 6.10.1 path wasn't yet pulled in as
a layer-shell-qt transitive, OR a subsequent rebuild promoted the
6.10.1 path into the closure.  Either way, NOW it's in the mirror
and the launcher's wholesale ``qt-6/plugins`` discovery picks it
up.

FIX:

1. Skip ANY ``/nix/store/*-qt*-*/lib`` dir in the LD_LIBRARY_PATH /
   QT_PLUGIN_PATH walk (qtbase, qtdeclarative, qt5compat, layer-
   shell-qt, kquickcharts, qtquickcontrols*, qttools, qtwayland --
   the full Plasma 6 transitive Qt6 closure).  None of those
   versions are guaranteed ABI-compatible with the installer's
   build-time Qt 6.8.1.

2. AFTER the nix-store walk completes, explicitly add the
   reprobuild-side qt6-base + qt6-declarative + qt6-quickcontrols2
   + qt6-tools plugin/qml dirs.  These are the EXACT 6.8.1 install
   trees the installer's RPATH points at, so the plugin ABI
   matches the linked Qt6Core/Gui/Qml ABI.

EVIDENCE:

  G2 install attempt #1 (clean, 00:27)  -> INSTALLER_RC=134, munmap
  G2 install attempt #2 (diag, 00:35)   -> same crash, strace tail
                                           shows munmap_chunk right
                                           after locale C->C.UTF-8
                                           message
  G2 install attempt #3 (37.7-only, 01:09) -> same crash, confirming
                                              the regression isn't
                                              in M9.R.37.8's cpp
                                              delta

Host run of the same binary outside QEMU -- no crash, Phase 1
reaches the ``repro hardware probe`` spawn.  This rules out the
binary itself + isolates the regression to the live-ISO-mounted
nix-store mirror's Qt 6.10.1 path being picked up by the launcher's
qt-6/plugins discovery.

The fix preserves M9.R.37.5's surgical-LD_LIBRARY_PATH approach +
extends the same surgical principle to QT_PLUGIN_PATH +
QML2_IMPORT_PATH: only Qt6 prefixes that match the installer's
build-time Qt version are wired in.

Author: zah

recipes/reproos-iso/scripts/stage-de-rootfs.sh

@@ -644,6 +644,29 @@ for d in /nix/store/*/lib; do
   case "$d" in
     /nix/store/*-glibc-*/lib) continue ;;
   esac
+  # M9.R.38.3 — skip ANY nix-store Qt6 prefix.  The installer is
+  # compiled + RPATH'd against ``/opt/repro/.../qt6-base/.repro/
+  # output/install/usr/lib/libQt6Core.so.6.8.1``, but the de-rootfs
+  # mirror also ships an UNRELATED ``zp6r9bxds...-qtbase-6.10.1/lib/``
+  # tree pulled in as a transitive of layer-shell-qt-6.5.3 (which is
+  # in the DE closure).  Without this skip the launcher's qt-6/plugins
+  # / qt-6/qml walk below picks up the 6.10.1 plugin tree as well, and
+  # the Qt 6.8.1 binary loading a 6.10.1 ``libqoffscreen.so`` /
+  # ``QtQuick.Controls`` plugin trips C++ ABI mismatch -> heap
+  # corruption -> ``munmap_chunk(): invalid pointer`` on init, SIGABRT
+  # before Phase 1.  The qt6-base + qt6-declarative + qt6-quickcontrols2
+  # the installer needs live at /opt/repro/... paths the RPATH already
+  # covers; no nix-store Qt6 mirror is required.
+  case "$d" in
+    /nix/store/*-qtbase-*/lib | \
+    /nix/store/*-qtdeclarative-*/lib | \
+    /nix/store/*-qt5compat-*/lib | \
+    /nix/store/*-layer-shell-qt-*/lib | \
+    /nix/store/*-kquickcharts-*/lib | \
+    /nix/store/*-qtquickcontrols*/lib | \
+    /nix/store/*-qttools-*/lib | \
+    /nix/store/*-qtwayland-*/lib) continue ;;
+  esac
   # M9.R.37.5: include ONLY dirs that ship a library the ``repro``
   # binary's Nim {.dynlib: "..."} pragma resolves by bare leaf name:
   #   * libclingo.so      (libs/repro_solver/.../clingo_bindings.nim)
@@ -682,6 +705,24 @@ for d in /nix/store/*/lib; do
     fi
   fi
 done
+# M9.R.38.3 — the installer's RPATH points to /opt/repro/.../qt6-base
+# /.repro/output/install/usr/lib/qt-6/plugins/ + qt6-declarative's
+# qt-6/qml/.  Wire those EXPLICITLY since the loop above only walks
+# /nix/store; without this Qt finds no plugins + falls back to system
+# Debian Qt6 (which doesn't exist in the live DE rootfs) + crashes on
+# QtQuick init.
+for repro_qt_pkg in qt6-base qt6-declarative qt6-quickcontrols2 qt6-tools; do
+  qtpkg_dir="/opt/repro/reprobuild/recipes/packages/source/${repro_qt_pkg}/.repro/output/install/usr/lib"
+  if [ -d "${qtpkg_dir}/qt-6/plugins" ]; then
+    _repro_qt_plugins="${qtpkg_dir}/qt-6/plugins${_repro_qt_plugins:+:$_repro_qt_plugins}"
+    if [ -d "${qtpkg_dir}/qt-6/plugins/platforms" ]; then
+      _repro_qpa_plugins="${qtpkg_dir}/qt-6/plugins/platforms${_repro_qpa_plugins:+:$_repro_qpa_plugins}"
+    fi
+  fi
+  if [ -d "${qtpkg_dir}/qt-6/qml" ]; then
+    _repro_qml_imports="${qtpkg_dir}/qt-6/qml${_repro_qml_imports:+:$_repro_qml_imports}"
+  fi
+done
 # Append caller-supplied paths last so any operator override wins.
 if [ -n "${LD_LIBRARY_PATH:-}" ]; then
   _repro_ldpath="$_repro_nix_libs:$LD_LIBRARY_PATH"