docs(series4): confirmed -- the cable came home with the failed unit

Removes the last caveat.  The Benfei (Prolific PL2303) on the bench is physically
the cable from the failed office setup, not a substitute picked up later.

The chain has no inference left: that cable is a PL2303; the Micromate USB host
has no Prolific driver in either firmware line; a laptop on the same cable and
modem round-trips perfectly; the Micromate on it never answered.  The FTDI cable
arriving 2026-09-26 is now a confirmation rather than a test.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ru8Lg9HkkYvX9VWWo65SmL

docs/micromate_protocol_reference.md

@@ -2143,10 +2143,18 @@ the failure began when the pair was split across two cables and one of them was
 the wrong chipset.  **One working and one not, set up side by side, is the
 signature of a mixed cable supply** — not of a unit fault.
 
-⚠ Still worth confirming: whether that cable travelled home *with* the unit, or
-was picked up separately at the bench.  If it travelled with it, there is no
-inference left.  Either way the FTDI cable arriving 2026-09-26 settles it — same
-unit, same modem, one variable.
+✅ **The cable travelled home with the unit** (confirmed 2026-09-25).  So the
+Benfei on the bench is physically the cable from the failed office setup — not a
+substitute picked up later.  There is no inference left in the chain:
+
+| | |
+|---|---|
+| the cable from the failed unit | **is** a Benfei / Prolific PL2303 |
+| the Micromate's USB host | has **no** Prolific driver, in either firmware line |
+| a laptop on that same cable + modem | round-trips perfectly |
+| the Micromate on it | never answered |
+
+The FTDI cable arriving 2026-09-26 is now a confirmation rather than a test.
 
 **Corollary worth knowing.**  The standing workaround — *"just deploy a Series III
 instead"* — works partly because a **MiniMate Plus has a DB-9 port directly on the