diff --git a/crates/Cross.toml b/crates/Cross.toml
index fe5ae7d4a..9016752b7 100644
--- a/crates/Cross.toml
+++ b/crates/Cross.toml
@@ -1,6 +1,8 @@
 # cross (https://github.com/cross-rs/cross) config for cross-compiling the
-# aarch64 `qbz` binary from an x86-64 Linux host. Used by
-# scripts/build-aarch64-linux.sh (CROSS mode).
+# aarch64 `qbzd` daemon from an x86-64 Linux host. Used by
+# scripts/build-aarch64-qbzd.sh (CROSS mode). The Qt desktop binary is NOT
+# cross-built (cxx-qt needs the target Qt's qmake at build time; see
+# scripts/build-aarch64-linux.sh) — build it natively on an ARM box.
 #
 # `image` pins a newer Ubuntu (cross 0.2.5's default aarch64 image is Ubuntu
 # 16.04 "xenial" — EOL, archived repos, OpenSSL 1.0.2 — which breaks modern
@@ -20,7 +22,7 @@ image = "ghcr.io/cross-rs/aarch64-unknown-linux-gnu:main"
 pre-build = [
     "dpkg --add-architecture arm64",
     "apt-get update",
-    "apt-get install -y --no-install-recommends pkg-config cmake clang libclang-dev nasm libasound2-dev:arm64 libjack-jackd2-dev:arm64 libfontconfig1-dev:arm64 libfreetype6-dev:arm64 libxkbcommon-dev:arm64 libwayland-dev:arm64 libxcb1-dev:arm64 libgl1-mesa-dev:arm64 libegl1-mesa-dev:arm64 libdbus-1-dev:arm64 libssl-dev:arm64",
+    "apt-get install -y --no-install-recommends pkg-config cmake clang libclang-dev nasm libasound2-dev:arm64 libjack-jackd2-dev:arm64 libdbus-1-dev:arm64 libssl-dev:arm64",
 ]
 
 [target.aarch64-unknown-linux-gnu.env]
diff --git a/scripts/build-aarch64-linux.sh b/scripts/build-aarch64-linux.sh
index f1982427a..47d741fc3 100755
--- a/scripts/build-aarch64-linux.sh
+++ b/scripts/build-aarch64-linux.sh
@@ -1,94 +1,124 @@
 #!/usr/bin/env bash
 #
-# build-aarch64-linux.sh — build the Linux aarch64 (ARM64) `qbz` binary, e.g.
-# for a Raspberry Pi 4 / other ARM single-board boxes.
+# build-aarch64-linux.sh — build the Linux aarch64 (ARM64) `qbz` binary (the
+# Qt frontend, package `qbz-qt`), e.g. for a Raspberry Pi 4 / other ARM boxes.
 #
-# ── READ FIRST: where can this run? ──────────────────────────────────────────
-# The generated Slint crate `qbz_ui` compiles as ONE ~1.6M-line module whose
-# single `rustc` needs ~30 GB RAM (RSS+swap). Consequences:
-#   • An 8 GB Mac or a 4 GB Pi CANNOT build it natively — it OOMs. Don't try.
-#   • Build on a box with >= ~16 GB RAM + swap (the wall is survivable at
-#     ~14 GB RAM + swap, proven on the dev box).
+# Rewritten 2026-08-25 for the Slint -> Qt frontend switch. There is no memory
+# wall any more: `qbz-qt` never pulls the 30 GB `qbz-ui` unit, so a 4 GB Pi
+# CAN build it natively (slowly). What the Qt build needs instead is a
+# **Qt >= 6.8 with private headers** — the cxx-qt RHI items include
+# <rhi/qrhi.h> — and the QtQuick.Effects / Qt.labs.qmlmodels QML modules at
+# run time. That is the distro gate:
+#   Debian 13+ (6.8), Ubuntu 25.04+ (6.8), Fedora 41+ (6.8), Arch/Gentoo: OK
+#   Ubuntu 24.04 (6.4, no Effects module), Debian 12, Fedora 40: NOT buildable
+#   with distro Qt — use the CI AppImage (Qt bundled) or aqt on a bigger box.
 #
-# This script has two modes, auto-selected by the host arch:
+# Modes, auto-selected by the host arch:
 #
-#   1. NATIVE  (running ON aarch64 Linux: an ARM runner, an ARM VM, etc.)
-#        -> apt-installs the build deps and runs `cargo build --release -p qbz`.
-#        This is exactly what a future Slint aarch64 CI job runs — treat the
-#        dep list + build line below as the workflow's source of truth.
+#   1. NATIVE  (running ON aarch64 Linux: a Pi, an ARM VM, the ARM CI runner)
+#        -> apt-installs the build deps (Qt from the distro), installs rustup
+#        if there is no cargo, runs `cargo build --release -p qbz-qt`, then
+#        prints the glibc floor and boots the binary offscreen (same criterion
+#        as CI: >= 10 log lines, zero QML complaints, QbzCore initialized).
+#        This mirrors .github/workflows/build-qt-linux.yml's aarch64 job, with
+#        distro Qt instead of aqt.
 #
-#   2. CROSS   (running on x86-64 Linux with Docker, e.g. the dev box, 30 GB)
-#        -> uses `cross` (https://github.com/cross-rs/cross): a container with
-#        the aarch64 sysroot + the arm64 dev libs (see crates/Cross.toml) does
-#        the compile. Needs Docker running and ~30 GB RAM available to it.
+#   2. CROSS   (on x86-64 Linux with Docker) — NOT SUPPORTED for the Qt binary.
+#        cxx-qt-build runs the TARGET Qt's `qmake -query` during the build,
+#        which needs qemu-user + binfmt_misc on the host, and cross-rs's
+#        images are Ubuntu 20.04 (Qt 5). A trixie-based cross image is
+#        possible but untested; until someone builds and proves it, this mode
+#        exits with that explanation instead of pretending. The qbzd script
+#        keeps its CROSS mode — the daemon links no Qt.
 #
-# macOS is intentionally NOT a build host here: cross from macOS to
-# linux-gnu means re-creating a full Linux sysroot for every native dep
-# (ALSA, dbus, fontconfig, …). Run the CROSS mode on a Linux box instead.
+# Memory: with <= 4 GB RAM the script forces CARGO_BUILD_JOBS=1 (one rustc at
+# a time). Expect 1-3 h on a Pi 4 cold. Override with JOBS=.
 #
 # Output: dist/qbz-aarch64-linux (an aarch64 ELF — verify with `file`).
 # ─────────────────────────────────────────────────────────────────────────────
 set -euo pipefail
 
-cd "$(dirname "$0")/.."          # repo root (qbz-nix)
+cd "$(dirname "$0")/.."          # repo root
 REPO="$(pwd)"
-TARGET="aarch64-unknown-linux-gnu"
 OUT="$REPO/dist/qbz-aarch64-linux"
+say() { printf '[aarch64-build] %s\n' "$*"; }
+die() { say "ERROR: $*" >&2; exit 1; }
 
-# The Linux build deps for the Slint `qbz` binary (kept in sync with the CI
-# workflows). PipeWire is reached through its ALSA/JACK compat shims, so only
-# libasound2-dev + libjack-jackd2-dev are needed.
+# Build deps for the Qt `qbz` binary — the same list as build-qt-linux.yml
+# minus what aqt provides there (here the distro's Qt provides it).
 DEPS=(
-  build-essential pkg-config cmake clang libclang-dev mold nasm
-  libasound2-dev libjack-jackd2-dev
-  libfontconfig1-dev libfreetype-dev
-  libxkbcommon-dev libwayland-dev libxcb1-dev
-  libgl1-mesa-dev libegl1-mesa-dev
-  libdbus-1-dev libssl-dev
+  build-essential pkg-config cmake clang libclang-dev nasm curl
+  libasound2-dev libjack-jackd2-dev libdbus-1-dev libssl-dev
+  libgl1-mesa-dev libegl1-mesa-dev libxkbcommon-dev
+  qt6-base-dev qt6-base-private-dev
+  qt6-declarative-dev qt6-declarative-private-dev
+  qt6-shadertools-dev
+  qml6-module-qtquick qml6-module-qtquick-controls qml6-module-qtquick-effects
+  qml6-module-qtquick-window qml6-module-qtqml-models qml6-module-qt-labs-qmlmodels
+  qt6-wayland qt6-qpa-plugins
 )
 
 arch="$(uname -m)"
 case "$arch" in
   aarch64 | arm64)
-    echo "[aarch64-build] NATIVE build on $arch"
+    say "NATIVE build on $arch ($(. /etc/os-release; echo "$PRETTY_NAME"))"
     if command -v apt-get >/dev/null; then
+      # The distro gate, checked before installing anything: a Qt below 6.8
+      # fails much later with a confusing "non-existent property" at runtime.
+      qtver="$(apt-cache policy qt6-base-dev | awk '/Candidate/ {print $2}' | grep -oE '^[0-9]+\.[0-9]+' || true)"
+      [[ -n "$qtver" ]] || die "no qt6-base-dev candidate — this distro has no Qt 6 (see header)"
+      if [[ "$(printf '%s\n' "$qtver" "6.8" | sort -V | head -1)" != "6.8" ]]; then
+        die "distro Qt is $qtver; the tree needs >= 6.8 (see header for the distro table)"
+      fi
+      say "distro Qt $qtver — OK"
       sudo apt-get update
       sudo apt-get install -y --no-install-recommends "${DEPS[@]}"
     else
-      echo "[aarch64-build] non-apt distro: install the equivalents of: ${DEPS[*]}" >&2
+      say "non-apt distro: install the equivalents of: ${DEPS[*]}" >&2
     fi
-    ( cd crates && cargo build --release -p qbz )
+    if ! command -v cargo >/dev/null && [[ ! -x "$HOME/.cargo/bin/cargo" ]]; then
+      say "no cargo — installing rustup (stable, minimal)"
+      curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --profile minimal --default-toolchain stable
+    fi
+    export PATH="$HOME/.cargo/bin:$PATH"
+    rustc -V; cargo -V
+
+    mem_mb="$(awk '/MemTotal/ {print int($2/1024)}' /proc/meminfo)"
+    if [[ -n "${JOBS:-}" ]]; then jobs="$JOBS"
+    elif (( mem_mb <= 4500 )); then jobs=1
+    else jobs="$(nproc)"; fi
+    say "RAM ${mem_mb} MB -> CARGO_BUILD_JOBS=${jobs}"
+    # No RUSTFLAGS, no mold, stable: same cache rule as qt-run.sh.
+    ( cd crates && CARGO_BUILD_JOBS="$jobs" CARGO_INCREMENTAL=0 cargo build --release -p qbz-qt )
     install -Dm755 "crates/target/release/qbz" "$OUT"
     ;;
   x86_64 | amd64)
-    echo "[aarch64-build] CROSS-compile from $arch via cross (Docker)"
-    if ! docker info >/dev/null 2>&1; then
-      echo "[aarch64-build] ERROR: Docker is not running. cross needs it." >&2
-      exit 1
-    fi
-    command -v cross >/dev/null || cargo install cross --locked
-    # Cap the container's RAM so a runaway qbz_ui rustc gets OOM-killed
-    # (losing the build) instead of swap-thrashing the host into a hard freeze
-    # — the dev box has no hibernation and dies under memory pressure. Override
-    # via CROSS_CONTAINER_OPTS if your box has more headroom.
-    # qbz-ui's Slint build imports fonts from the REPO ROOT (../../../../static/
-    # fonts/*.ttf) — outside the `crates/` workspace that cross mounts. Mount
-    # static/ at its host path so those relative imports resolve in the
-    # container (cross 0.2.x mounts the project at the host path).
-    # qbz_ui's single rustc demands ~30-33 GB (RSS+swap). --memory-swap must
-    # exceed that or Docker OOM-kills the build; 48g leaves headroom yet still
-    # caps a runaway well under the host's 30G RAM + 46G swap (no freeze). RAM
-    # cap 24g keeps ~6g for the desktop (overflow swaps, doesn't exhaust).
-    export CROSS_CONTAINER_OPTS="${CROSS_CONTAINER_OPTS:---memory=24g --memory-swap=48g} --volume $REPO/static:$REPO/static:ro"
-    # Cross.toml (workspace root) injects the arm64 dev libs into the image.
-    ( cd crates && cross build --release --target "$TARGET" -p qbz )
-    install -Dm755 "crates/target/$TARGET/release/qbz" "$OUT"
+    die "CROSS mode is not supported for the Qt binary (see the header: cxx-qt \
+needs the target Qt's qmake at build time -> qemu-user + a Qt>=6.8 arm64 \
+sysroot). Build natively on an ARM box, or dispatch release-linux-aarch64.yml."
     ;;
   *)
-    echo "[aarch64-build] ERROR: unsupported build host arch: $arch" >&2
-    exit 1
+    die "unsupported build host arch: $arch"
     ;;
 esac
 
-echo "[aarch64-build] done -> $OUT"
+say "done -> $OUT"
 file "$OUT" || true
+say "glibc floor: $(objdump -T "$OUT" | grep -oE 'GLIBC_[0-9]+\.[0-9]+' | sort -Vu | tail -1)"
+
+# The smoke, same criterion as CI. Distro Qt is on the default paths, so no
+# env is needed beyond the offscreen platform.
+if [[ "${SMOKE:-1}" == 1 ]]; then
+  log="$(mktemp "${TMPDIR:-/tmp}/qbz-aarch64-smoke-XXXXXX")"
+  say "offscreen smoke (60 s) -> $log"
+  QT_QPA_PLATFORM=offscreen RUST_LOG=info timeout 60 "$OUT" > "$log" 2>&1 || true
+  lines="$(wc -l < "$log")"
+  (( lines >= 10 )) || { cat "$log"; die "smoke: the app did not start ($lines lines)"; }
+  errs="$(grep -av 'propertyCache' "$log" | grep -aciE 'is not a type|unavailable|ReferenceError|TypeError|Cannot read|Unable to assign|Cannot open|no such method|non-existent property|failed to load component|is not installed' || true)"
+  if (( errs > 0 )); then
+    grep -av 'propertyCache' "$log" | grep -aiE 'is not a type|unavailable|ReferenceError|TypeError|Cannot read|Unable to assign|Cannot open|no such method|non-existent property|failed to load component|is not installed' | head -20 >&2
+    die "smoke: $errs QML complaint(s)"
+  fi
+  grep -aq 'QbzCore initialized' "$log" || { tail -20 "$log" >&2; die "smoke: never reached QbzCore init"; }
+  say "smoke OK (0 QML complaints, core initialized)"
+fi
diff --git a/scripts/build-aarch64-qbzd.sh b/scripts/build-aarch64-qbzd.sh
index ddc0227aa..590724d3b 100755
--- a/scripts/build-aarch64-qbzd.sh
+++ b/scripts/build-aarch64-qbzd.sh
@@ -4,13 +4,14 @@
 # e.g. for a Raspberry Pi 4 + HiFiBerry/USB DAC streamer.
 #
 # ── Why this is NOT build-aarch64-linux.sh ───────────────────────────────────
-# That script builds the Slint desktop `qbz`, whose generated `qbz_ui` crate is
-# ONE ~1.6M-line module needing ~30 GB for a single rustc. `qbzd` is the
-# slint-free column of the workspace: no UI crate, no fonts, no GPU libs. It
-# builds in minutes and fits on modest hardware, so:
-#   • a 4 GB Pi CAN build it natively (unlike the desktop binary);
-#   • the container caps here are small — no 48 GB swap headroom needed;
-#   • the `static/` fonts mount the desktop script needs is irrelevant.
+# That script builds the Qt desktop `qbz`, which needs a Qt >= 6.8 with private
+# headers on the build host and cannot be cross-compiled with cross-rs (the
+# target Qt's qmake has to run during the build). `qbzd` is the Qt-free and
+# Slint-free column of the workspace: no UI crate, no fonts, no GPU libs. It
+# builds in minutes on modest hardware and cross-compiles cleanly, so:
+#   • a 4 GB Pi CAN build it natively;
+#   • CROSS mode via cross-rs + crates/Cross.toml still works here;
+#   • the container caps are small.
 #
 # Two modes, auto-selected by host arch (same shape as the desktop script):
 #
@@ -62,9 +63,8 @@ case "$arch" in
     # the same as the desktop script's — a runaway gets killed instead of
     # swap-thrashing this box (30 GB, no hibernation) into a hard freeze.
     export CROSS_CONTAINER_OPTS="${CROSS_CONTAINER_OPTS:---memory=8g --memory-swap=12g}"
-    # crates/Cross.toml injects the arm64 dev libs into the image. It installs
-    # the desktop's superset (GUI libs included) because it is keyed by TARGET,
-    # not by crate — harmless here, and not worth forking a second image.
+    # crates/Cross.toml injects the arm64 dev libs into the image (the daemon's
+    # set; the Qt desktop is not cross-built, see build-aarch64-linux.sh).
     ( cd crates && cross build --release --target "$TARGET" -p qbzd )
     install -Dm755 "crates/target/$TARGET/release/qbzd" "$OUT"
     ;;