research: the eight ASSIGN blocks per memory, and a MIDI assignments editor

[AliceLafox]

What

Every memory in a MEMORY*.RC0 carries eight <ASSIGN1..8> blocks, each with the
same six fields:

<ASSIGN1>
	<Sw>0</Sw>
	<Source>0</Source>
	<SourceMode>0</SourceMode>
	<Target>0</Target>
	<TargetMin>0</TargetMin>
	<TargetMax>1</TargetMax>
</ASSIGN1>

This is the pedal's MIDI control surface: the RC series has no fixed CC
implementation chart at all — a player maps a CC number to a function through
ASSIGN 1-8, with CC#1-31 and 64-95 assignable and a source mode of MOMENT or
TOGGLE. Editing that on the hardware means a menu inside a menu, eight slots deep,
repeated per memory. It is exactly the kind of thing a companion app should own.

LooperCat touches these blocks nowhere today: a grep over core/, app/ and
fixtures/ finds no reference to ASSIGN.

State of knowledge

Confirmed by reading a real card: the block layout and field names above, and that
the eight blocks exist per memory for all 99 memories.

Not yet known, and needed before any editor:

• Whether the RC-5 carries the same eight blocks. No RC-5 RC0 sample is checked
  into this repo, and fixtures/golden.json records only TRACK1 / MASTER / RHYTHM.
  This is the first question to settle, since the RC-5 is the pedal we support.
• The enum maps behind Source and Target — which integer means which CC number
  and which means which function. The vendor Parameter Guide documents the target
  list in prose; the numeric encoding has to be pinned against hardware.
• Whether TargetMin / TargetMax are raw parameter values or an index into the
  target's own range.

Research plan

1. Dump a memory pair, change one assignment on the pedal, dump again, diff. The
   same differential method that pinned the Count-In triple — it yields exact
   values rather than an interpretation of documentation.
2. Repeat per field until Source and Target are mapped, recording each value
   with the capture that proves it.
3. Only then design the editor. As with the memory editor, usecase-first: the
   assignments a player actually wants ("a footswitch that starts the rhythm")
   before an eight-row grid of raw enums.

Notes

Related to #23 (can the pedal be told to save a loop over MIDI) — same MIDI tier,
different question: #23 is about commanding the pedal live, this is about the
assignments stored on the card.

[AliceLafox]

The first open question is settled: the RC-5 carries no per-memory control blocks. A real RC-5 MEMORY1.RC0 has no <CTL>, no <ASSIGN> and no <LOOPFX> in any of its 99 memories.

Its control map is device-wide and lives in SYSTEM1/2.RC0 instead, next to the MIDI settings:

<MIDI>  RxCtlCh Omni RxNoteCh TxCh Sync ClkOut SyncStart PcOut MidiThru UsbThru </MIDI>
<CTL>   Pedal1 Ctl1 Ctl2 Exp Cc80 Cc81 Cc82 Cc83 Cc84 Cc85 Cc86 Cc87 </CTL>

On the RC-5 the CC numbers are fixed at 80–87 and only the function behind each one is chosen, which matches the reference manual's CC#80–87 FUNC list. So for this pedal the editor is a device-wide one over SYSTEM*.RC0, not a per-memory one.

That changes the research plan above in one place: SYSTEM*.RC0 has the same two-bank layout and write-counter trailer as the memory files, but the app has never written it. Before any editor, the first write has to be proven on hardware — the pedal must still boot, and MemoryNumber (the pedal's own record of the current memory) must survive untouched.