Bluetooth mic startup: honest Listening indicator, startup-time investigation

The bar turned green after 2 s on a timer even when the microphone delivered
nothing. It now turns green only on real audio: RMS above 0.0005, or three
consecutive chunks that are not digital silence (the virtual mic emits one
stray nonzero chunk right after start, and a Bluetooth headset's floor ramps
in from a few LSB). Measured 1.2-1.4 s after the key, within 0.14 s of the
first real samples.

diagnostics/bluetooth/ records how startup went from ~1.6 s (or never) to
~1.1-1.4 s: a btusb driver bug, two PipeWire bluez5 bugs, a 500 ms WirePlumber
switch timeout and an over-broad auto-connect rule. Those fixes are machine
level and live outside this repo; the patches, tools and measurements are here.
STARTUP-TIME.md is the summary and explains the ~0.9 s hardware floor.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Xoc9DJCViR7dg9eKzzAcfQ

diagnostics/bluetooth/tools/repro-loop.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+# Restart WirePlumber, run a traced trial, stop when the kernel logs submission failed (90).
+SC=$(dirname "$0")
+for i in 1 2 3 4 5 6; do
+  systemctl --user restart wireplumber; sleep 9
+  /home/tank/repos/speech-to-text/bin/stt status --json | grep -q '"state": *"idle"' || { echo "stt busy"; break; }
+  T0=$(date +%s)
+  "$SC/trial.sh" "repro-$i" > "$SC/repro-$i.log" 2>&1
+  if sudo -n journalctl -k --since "@$T0" --no-pager | grep -q 'submission failed (90)'; then echo "REPRODUCED on attempt $i"; exit 0; fi
+  echo "attempt $i: no failure"; sleep 3
+done
+echo "not reproduced"