The bug behind "no sound on d5 in perfect.tidal, meter moves, master silent,
plays a bar then slowly fades to zero, then crackles". Also, finally, the
true root of #21 — which was diagnosed as a missing `djfbus` and fixed as
"safe at rest (0)", when the actual defect was one layer deeper.

FINDING, proven by queryArc against an empty controls map (not by ear):

    gF1 $ sound "bd", knob never touched  ->  SILENT (no events)
    gMask  untouched                      ->  SILENT
    gMute3 untouched                      ->  SILENT
    gain ("^77" * 1.3) untouched          ->  SILENT
    gPanic untouched                      ->  SILENT

A bare `"^NN"` whose CC has never arrived does NOT default to 0 — it yields
NO EVENTS AT ALL. And `#` (i.e. `|>`) cannot emit without a value on its
right-hand side, so the entire stream disappears. Every g*-wrapped stream in
the corpus is therefore silent until that physical control is moved once.

This is why "move all the controls" was always step one of a gig, and why
PLN's rig felt fine for months: the habit was masking a mute-bomb. Today's
BootTidal restart (to pick up the 77903244 DJF fix) wiped the control map and
re-armed it across the whole surface at once — so the fix appeared to make
things worse.

It also explains the odd "plays one bar then slowly fades to zero": `dN` is
`xfade N`, which crossfades the outgoing pattern out over 4 cycles while
fading the new one in. The new one had no events, so what PLN heard was the
OLD pattern dying gracefully into nothing — meter moving throughout, master
quiet once the fade completed. The symptom looked like a filter closing;
it was a crossfade to silence.

TWO-LAYER FIX, because one layer cannot reach everything:

1. `orDef` in the helper let-block — substitutes a default when a control
   pattern is empty. Applied to gDJF (0.5 = centre = true bypass),
   midiOn/midiOff/midiNo/midiBoth (0/1/1/0 = "not pressed"), midiGGlobal
   (0.769, so *1.3 == unity rather than 0), and gPanic (0 = normal, not
   silent). It must live at the HELPER level, not per call site, because
   tracks combine controls arithmetically — `midiOn ("^34" - "^18")` in
   perfect.tidal:63 — and `touched - untouched` is itself empty, so a
   per-CC default could never catch it.

2. Boot-time control seeding via `setF` — the corpus-wide half. `orDef`
   cannot reach the 1860 sites across 343 track files that apply controls
   directly (`# crushbus 41 (range 16 3.5 "^53")`). Editing those is
   #46-scale work. Seeding every LCXL control at boot fixes all of them at
   once while touching no track file; a real CC overwrites its seed the
   instant the knob moves.

Seed policy follows the authoring convention `range <neutral> <extreme>`,
so 0 == neutral: A/B knobs 0, C1-C3 0.5 (DJF centre), C4-C8 0, fader 77
0.769 (unity), faders 78-84 1.0 (gains open = audible), all buttons 0.

Seed coverage was verified by set-difference, not assumed: 49 seeded vs 54
distinct "^NN" in live/. The 5 stragglers were each resolved rather than
waved off — ^45 needs no seed (it flows through midiOn, so orDef covers
it), ^6 and ^61 are commented out at their only call sites, and ^1 (an
external keyboard modwheel) and ^21 were added explicitly.

Verification of the fix, all four knob positions, via an explicit controls
map — untouched now bypasses and NO touched behaviour changed:

    untouched -> cutoff=20000 hcutoff=20     (was: SILENT)
    at 0.0    -> cutoff=180   hcutoff=20     (low-pass to subbass)
    at 0.5    -> cutoff=20000 hcutoff=20     (bypass)
    at 1.0    -> cutoff=20000 hcutoff=8000   (high-pass to superhigh)
    gMute3 pressed -> SILENT                 (mute still mutes)
    gPanic armed   -> gain 0.0               (panic still panics)

tools/check-boot.sh gains a second pass over the seed block (pinning the
`streamSetF :: Stream -> String -> Pattern Double -> IO ()` signature it
calls through), so neither half of this can rot silently. Its own first
attempt at that pass was itself broken — a sed that produced
`_seed = _seed = concat` — and the checker caught it. Same lesson as
77903244: run the guard, don't trust that you wrote it correctly.

prelude.tidal (the stale-boot rescue sheet) carries the matching orDef form
plus a ready-to-eval `_seedNow` list, for the case where a gig laptop boots
silent and the cheapest fix is one paste rather than sweeping 40 controls.