audio: select the pipewire backend explicitly and ban the pulse one

Full-system audit findings: without an explicit provider selection the
image installed real PulseAudio (Plasma Mobile hard-path), which claims
the card and ships a wireplumber fragment disabling hardware.audio -
zero sinks forever. Mirror the dev phone's world: pipewire backend meta
+ pipewire-pulse + echo-cancel in extra_packages, pulse meta banned via
apk conflict in fp6-device-tweaks. The two hand-made /etc audio
fragments (wireplumber no-ACP rule, AEC pair for VoLTE speakerphone)
move into soc-fairphone-fp6-audio.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

aports/device/soc-fairphone-fp6-audio/50-echo-cancel.conf

@@ -0,0 +1,30 @@
+# Acoustic echo cancellation for VoLTE speakerphone calls (journal/ims.md s43).
+# Creates a virtual pair: ec_sink (play here; forwarded to the speakers and
+# used as the AEC reference) and ec_source (mic with the speaker signal
+# subtracted, WebRTC AEC). capture/playback are pinned to the hardware nodes
+# so making ec_* the defaults cannot loop the module into itself.
+context.modules = [
+    {   name = libpipewire-module-echo-cancel
+        args = {
+            library.name = aec/libspa-aec-webrtc
+            source.props = {
+                node.name = "ec_source"
+                node.description = "Echo-cancelled microphone"
+            }
+            sink.props = {
+                node.name = "ec_sink"
+                node.description = "Echo-cancelled speakers"
+            }
+            capture.props = {
+                node.name = "ec_capture"
+                target.object = "alsa_input.platform-sound.capture.1.0"
+                node.passive = true
+            }
+            playback.props = {
+                node.name = "ec_playback"
+                target.object = "alsa_output.platform-sound.playback.0.0"
+                node.passive = true
+            }
+        }
+    }
+]

aports/device/soc-fairphone-fp6-audio/51-fp6-ucm.conf

@@ -0,0 +1,11 @@
+monitor.alsa.rules = [
+  {
+    matches = [ { device.name = "alsa_card.platform-sound" } ]
+    actions = {
+      update-props = {
+        api.alsa.use-acp = false
+        api.alsa.soft-mixer = false
+      }
+    }
+  }
+]

aports/device/soc-fairphone-fp6-audio/APKBUILD

@@ -5,7 +5,7 @@
 # The tplg/UCM target filenames contain spaces, hence the safe source names.
 maintainer="Jorijn van der Graaf <jorijnvdgraaf@catcrafts.net>"
 pkgname=soc-fairphone-fp6-audio
-pkgver=1
+pkgver=2
 pkgrel=0
 pkgdesc="Fairphone 6 audio topology, amp firmware and UCM profile"
 url="https://forgejo.catcrafts.net/Catcrafts/audioreach-topology"
@@ -17,6 +17,8 @@ source="
 	aw88261_acf.bin
 	ucm-milos-fp6.conf
 	HiFi.conf
+	51-fp6-ucm.conf
+	50-echo-cancel.conf
 "
 
 package() {
@@ -28,6 +30,12 @@ package() {
 		"$pkgdir/usr/share/alsa/ucm2/conf.d/milos/Fairphone (Gen. 6).conf"
 	install -Dm644 "$srcdir"/HiFi.conf \
 		"$pkgdir"/usr/share/alsa/ucm2/Fairphone/fp6/HiFi.conf
+	# wireplumber: no ACP/soft-mixer for the UCM-driven card
+	install -Dm644 "$srcdir"/51-fp6-ucm.conf \
+		"$pkgdir"/etc/wireplumber/wireplumber.conf.d/51-fp6-ucm.conf
+	# AEC pair (ec_sink/ec_source) for VoLTE speakerphone calls
+	install -Dm644 "$srcdir"/50-echo-cancel.conf \
+		"$pkgdir"/etc/pipewire/pipewire.conf.d/50-echo-cancel.conf
 }
 
 sha512sums="
@@ -35,4 +43,6 @@ sha512sums="
 a84b0595ae71b0bb594034a9f5fd77b984c9086cd917f32524c4b5172bc72a426e5d188d18dbccdb587f66d60fa15cad441fffcd48a3a1ce66335199b61e0350  aw88261_acf.bin
 3bb268f9fcb8d1c0b42741b67da42b6361bab259e7211d9930919995ebe7dcf67826e6d4f00ff5e4fe5b52067fe90d00212158c3b4879d1bee481e87f0623206  ucm-milos-fp6.conf
 2a189c3141fedc43f8eb19f4df1e43487223d524e27da3f948556d224cca1f493f6815ada191953fb79a19d5c5abadb21de7b3ece7b74b0929338c216e21e84a  HiFi.conf
+28a301e7eed738408660c1a303771a6cd1bc2bdd493bac95602f17c9b2cb56a0b9c0001b8002a99b0b1bd3dc1d2ee3f6696a8b629b86818d64605c643d2eec29  51-fp6-ucm.conf
+ec63fa5363738a43c9eee4b1be70201e2d2076ec817031fda087e61d781e81dc67351be44faf8b056a2939875a139cd909f7c311115bb1150e17ad4493846606  50-echo-cancel.conf
 "