test(boot): check-boot now RUNS the helpers against an empty control map (#55)

PLN asked what tooling would have caught tonight's mute-bomb. Honest answer:
nothing we had, and not tidal-ears — it analyses audio, and this bug produced
SILENCE. Silence is indistinguishable from silence no matter how well measured.
The defect was symbolic: a pattern emitting zero events.

Typechecking could not catch it either. `gF1 $ sound "bd"` is perfectly
well-typed while producing NO EVENTS, because an untouched "^NN" yields nothing
and `#` cannot emit without a right-hand value. Pass 1 of this script was green
throughout the entire outage.

The missing capability was the ability to ask one question mechanically:
"what does this helper do with an EMPTY control map?" — i.e. on a fresh boot,
before any knob has moved. That is now pass 3: it extracts the helper block,
appends assertions, compiles, and RUNS them, checking that each of gF1/gF2/gF3,
gMask, gMute1-3, gM1-3, gPanic, midiGdef and a composed gF1.gM2 stack all emit
events with `State (Arc 0 1) M.empty`.

It is a real execution rather than a typecheck, but pure pattern evaluation
only: no stream, no scsynth, no MIDI, no port binding. Safe to run mid-set.

Verified in BOTH directions, which is the whole point:
  - current BootTidal.hs        -> 13/13 audible, exit 0
  - orDef guards stripped out
    (i.e. the pre-3685c743 code) -> 11 FAILs naming each silent helper, exit 1

That negative test also confirmed something useful about the shape of the bug:
gPanic and midiGdef stayed audible even with the guards stripped, because they
route through `range`/arithmetic that survives an empty map differently from
`#`. So a partial fix would have looked partially fine — exactly the kind of
half-green result that lets a bug like this hide for months.

Turns the ad-hoc Haskell probe written during the incident into a permanent
regression test. This bug class has now bitten three times (#21 djfbus, #48's
one-directional filters, #55's untouched-control silence); pass 3 is the first
thing that would have caught any of them before a boot.

tools/check-boot.sh

@@ -97,6 +97,82 @@ if [ -n "$SEED_START" ]; then
     exit 1
   fi
   echo "check-boot: OK — #55 control-seed block typechecks."
+
+  # --- Pass 3: RUN the helpers against an EMPTY control map (#55) ----------
+  # The regression test that tonight's bug needed and nobody had. Typechecking
+  # cannot catch it: `gF1 $ sound "bd"` is perfectly well-typed while emitting
+  # ZERO events, because an untouched "^NN" yields nothing and `#` cannot emit
+  # without a right-hand value. The only mechanical check is to QUERY the
+  # pattern with no controls set and assert events come out.
+  #
+  # This is a real execution, not a typecheck — but it is pure pattern
+  # evaluation: no stream, no scsynth, no MIDI, no ports. Safe mid-set.
+  {
+    echo '{-# LANGUAGE OverloadedStrings #-}'
+    echo '{-# OPTIONS_GHC -Wno-missing-signatures -Wno-name-shadowing -Wno-type-defaults #-}'
+    echo 'module Main where'
+    echo 'import Sound.Tidal.Context'
+    echo 'import qualified Data.Map.Strict as M'
+    echo 'import System.Exit (exitFailure)'
+    echo 'import Data.IORef'
+    echo 'p :: Int -> ControlPattern -> IO ()'
+    echo 'p = undefined'
+    echo 'setI :: String -> Pattern Int -> IO ()'
+    echo 'setI = undefined'
+    sed -n "${START},${END}p" "$BOOT" | sed -e '1s/^let //' -e 's/^    //'
+    cat <<'HS'
+
+-- Query with a DELIBERATELY EMPTY controls map: the state of a fresh boot
+-- before any knob has been moved.
+audible :: String -> ControlPattern -> IORef Bool -> IO ()
+audible label pat failed = do
+  let evs = query pat (State (Arc 0 1) M.empty)
+  if null evs
+    then do putStrLn ("  FAIL " ++ label ++ " -> SILENT with an empty control map")
+            writeIORef failed True
+    else putStrLn ("  ok   " ++ label ++ " -> " ++ show (length evs) ++ " event(s)")
+
+main :: IO ()
+main = do
+  failed <- newIORef False
+  putStrLn "  (untouched-control audibility, #55)"
+  mapM_ (\(l, f) -> audible l (f (sound "bd")) failed)
+    [ ("gF1   ", gF1), ("gF2   ", gF2), ("gF3   ", gF3)
+    , ("gMask ", gMask)
+    , ("gMute1", gMute1), ("gMute2", gMute2), ("gMute3", gMute3)
+    , ("gM1   ", gM1), ("gM2   ", gM2), ("gM3   ", gM3)
+    , ("gPanic", gPanic)
+    ]
+  -- Gain paths: silent here means the global fader zeroes the whole rig.
+  audible "midiGdef" (sound "bd" # midiGdef) failed
+  -- A composed stack is the realistic shape a track actually uses.
+  audible "gF1.gM2 " (gF1 (gM2 (sound "bd"))) failed
+  bad <- readIORef failed
+  if bad then exitFailure else return ()
+HS
+  } > "$WORK/RunCheck.hs"
+  set +e
+  ROUT="$(ghc -package tidal -package containers -o "$WORK/runcheck" \
+            -outputdir "$WORK/out" "$WORK/RunCheck.hs" 2>&1)"
+  RRC=$?
+  set -e
+  if [ "$RRC" -ne 0 ]; then
+    echo "" >&2
+    printf '%s\n' "$ROUT" | sed "s#$WORK/RunCheck.hs#<run-check>#" >&2
+    echo "check-boot: FAIL — could not build the untouched-control test." >&2
+    exit 1
+  fi
+  set +e
+  "$WORK/runcheck"
+  RUNRC=$?
+  set -e
+  if [ "$RUNRC" -ne 0 ]; then
+    echo "check-boot: FAIL — helpers go SILENT with an untouched controller." >&2
+    echo "            This is the #55 mute-bomb. Streams will have no sound on" >&2
+    echo "            a fresh boot until every knob is physically moved." >&2
+    exit 1
+  fi
+  echo "check-boot: OK — all g* helpers audible with an untouched controller."
 else
   echo "check-boot: WARN — no #55 control-seed block found (untouched knobs" >&2
   echo "            will silence their streams; see BootTidal.hs history)." >&2