fix(modbus): review r1 - resolved address keys win only when the editor pinned them

N1: the m2 precedence trusted region/address whenever the keys were present,
but the AdminUI model stamps defaulted HoldingRegisters/0 on every save, so a
string-only tag (CSV import, or any editor toggle) silently became HR[0] -
reads AND writes. The resolved keys are now authoritative only when the editor
marked them ("addressResolved": true, written by Resolve); an unmarked
addressString is always resolved through the parser with the driver's family.
The model no longer stamps address fields for a string-only tag, CSV export
leaves its address cells blank, and the editor hint distinguishes string-only
from pinned tags. Tests: CSV import and editor save of a string-only tag, a
stamped-default blob, and the pinned positive control across families.
n1: docs/v2/modbus-addressing.md updated (FC23 opt-in, maxReadGap semantics,
coalescing scope, addressString/family rules, coil coercion, refusals).
n2: form round-trip tests for UseFC23ForMultiRegisterWrites /
DisableReadCoalescing. n4: the editor keeps unresolved address text when the
parent echoes back its own emit. n3: noted, no change.

Refs #741
Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT

docs/v2/modbus-addressing.md

@@ -149,7 +149,11 @@ Beyond per-tag addressing, `ModbusDriverOptions` exposes (#139–#143):
 - `UseFC15ForSingleCoilWrites` — force FC15 (write multiple coils
   qty=1) for single-coil writes. Safety/audit PLCs may require this.
 - `UseFC16ForSingleRegisterWrites` — same for FC16 vs FC06.
-- `DisableFC23` — kill switch for FC23 (currently unused; reserved).
+- `UseFC23ForMultiRegisterWrites` (default `false`) — opt-in: a 2–121-register
+  holding write is sent as one FC23 (write + read-back). A unit answering
+  exception 01 moves to FC16 until the next re-init. Without the key the
+  wire stays FC16 (#741).
+- `DisableFC23` — hard kill switch: never send FC23, even when opted in.
 
 ### Subscribe (#141)
 - Per-tag `Deadband` — suppress sub-threshold publishes on numeric tags.
@@ -165,9 +169,13 @@ Beyond per-tag addressing, `ModbusDriverOptions` exposes (#139–#143):
   this tag in isolation regardless of `MaxReadGap`).
 
 ### Block-read coalescing (#143)
-- `MaxReadGap` (default 0 = off) — gap budget the planner is willing to
-  bridge between adjacent register tags. With `MaxReadGap=10`, three tags
-  at HR 100/102/110 collapse into one FC03 of quantity 11.
+- `MaxReadGap` — gap budget the planner is willing to bridge between
+  adjacent tags of one (unit, region). With `MaxReadGap=10`, three tags at
+  HR 100/102/110 collapse into one FC03 of quantity 11. An explicit `0` =
+  coalescing off (its historical meaning); the default `8` applies only when
+  the key is absent (#741). Coils / DiscreteInputs (gap in bits), `String`
+  scalars and same-word `BitInRegister` tags coalesce too.
+- `DisableReadCoalescing` — turn coalescing off regardless of the gap.
 
 ### Coalescing auto-recovery (#148 / #150 / #151 / #152)
 - A coalesced read that fails with a Modbus exception (write-only or
@@ -231,3 +239,22 @@ the current Kepware "Modbus Ethernet Driver Help" PDF and Ignition's
 "Modbus Addressing" user-manual page — if a critical tool's mnemonics
 have shifted, add aliases in `ModbusAddressParser.TryParseType` rather
 than asking users to rewrite spreadsheets.
+
+
+## Address strings, families and region/type rules (#741)
+
+- A tag's `addressString` is resolved through `ModbusAddressParser` with the
+  **driver's** `Family` / `MelsecSubFamily`. When the AdminUI editor resolves
+  it ("Resolve with driver family") it persists the resolved
+  `region`/`address`/type fields plus `"addressResolved": true`; those pinned
+  fields are then authoritative, so a later family change never remaps the
+  tag. A blob with an **unmarked** `addressString` (CSV / API authoring) is
+  always resolved from the string — any `region`/`address` beside it is
+  ignored, so it can never collapse onto HR[0]. Editing a resolved field by
+  hand drops the string.
+- Coils / DiscreteInputs carry only Bool. A bit-region tag persisted with a
+  register `dataType` (the pre-#741 editor saved `Int16`) is coerced to Bool,
+  never refused. A register region with `Bool` is refused (use
+  `BitInRegister`).
+- Exception 01/02/03 are device refusals: per-tag Bad, one Warning per tag,
+  no driver Degraded; reads and writes share one comms-fault health slot.