docs: geom_honoured is asserted but not wired anywhere yet

The ring-geometry note claimed a rejected BP/RHBP is "observable rather than
silent".  That is overstated: geom_honoured exists on RXFrameAssembler and the
tests check it, but BBATop wires it to nothing -- no status register, no LED,
no UART line -- so a rejected geometry is silent to both the GC and the bench.
Recorded as a loose end; the guarantee today is "rejected rather than obeyed",
not "reported".

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/bba_compat_todo.md

@@ -66,10 +66,17 @@ driver's smaller ring is respected instead of ignored.
 
 **Garbage is rejected, not obeyed.** The bounds are used only when
 `bp >= 1` (page 0 is the TX buffer), `rhbp <= 0x0F` and `rhbp > bp`;
-otherwise the hardcoded pages 1–15 stand and `geom_honoured` goes low, so a
+otherwise the hardcoded pages 1–15 stand and `geom_honoured` goes low.
-mismatch is observable rather than silent. Without that check, `BP = 0` or an
+Without that check, `BP = 0` or an `RHBP` below `BP` gives a zero or negative
-`RHBP` below `BP` gives a zero or negative ring size and the assembler writes
+ring size and the assembler writes outside it.
-outside it.
+
+⚠️ **`geom_honoured` is NOT yet observable from outside the FPGA.** It is
+declared on `RXFrameAssembler` and asserted correctly (T7/T7b check it), but
+`BBATop` does not wire it to anything — no status register, no LED, no UART
+line. So a rejected geometry is currently silent to the GC and to the bench.
+Wiring it to the `StatusPanel` or the UART console is a small loose end worth
+closing; until then "rejected rather than obeyed" is the guarantee, not
+"reported".
 
 ⚠️ **A ring must be LARGER than `_MAX_FRAME_PAGES` (6) or nothing is ever
 stored.** A frame's length is unknown until EOF, so the assembler reserves the