feedback: plasma box, explicit fonts, and per-position text coalescing

Three endpoint gaps, found building the Descent 3 score overlay - the boxed
place|score field the original games drew over the callsign:

plasma box <x> <y> <w> <h> draws an outlined box with a blanked interior, the
overlay chrome, as one ESC P graphics write. The wire addresses whole bytes
horizontally, so the write covers the byte-aligned span containing the box and
clears span pixels outside it; documented, with 8-px alignment the advice.
Boxes queue FIFO with rows.

plasma text gains an explicit font: a third numeric token after the position,
with text still following, so `plasma text 2 2 7` still displays "7". Auto-fit
picks the font by LENGTH - short text always rendered large, and a "1" that
must fit a 12-px box simply could not be sent before. ResolvePosText
generalizes the legacy Score-font special case: 0 = auto, nonzero honored.

Text coalescing is now per position. The global rule - any queued text
superseded every other queued text - meant the documented two-field layout
(callsign top, score bottom) could not survive its own send burst: the second
field silently ate the first whenever both were queued. A newer text now
replaces only a queued text at the same (x,y).

15 new tests; 472 pass.

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

docs/FEEDBACK.md

@@ -43,11 +43,12 @@ case-insensitive. Lines over 256 bytes and UDP datagrams over 4 KB are dropped.
 
 ```
 # comment (also ;)
-lamp <addr> <state>       set one lamp
-lamp-all <state>          set every lamp
-plasma text [x y] <text>  write text to the plasma display
-plasma clear              clear the plasma display
-plasma row <y> <hex32>    write one full 128-px bitmap row
+lamp <addr> <state>              set one lamp
+lamp-all <state>                 set every lamp
+plasma text [x y [font]] <text>  write text to the plasma display
+plasma clear                     clear the plasma display
+plasma row <y> <hex32>           write one full 128-px bitmap row
+plasma box <x> <y> <w> <h>       outlined box with a blanked interior
 ```
 
 - **`<addr>`** — RIO lamp address, decimal or `0x` hex. Valid: `0x00–0x47`
@@ -62,17 +63,30 @@ plasma row <y> <hex32>    write one full 128-px bitmap row
   (`"VIPER 1-1"`; quotes stripped, no escapes). Two leading *numeric* tokens
   are a cursor position `x y`; omitted (or `0 0`) auto-fits and centers
   (`PlasmaPosText`). To display something that starts with two numbers, quote
-  it. Encoding is **Latin-1** (one byte = one char, the plasma's wire
-  encoding) — do not send UTF-8 for accented characters.
+  it. A **third** numeric token after the position — with text still following
+  — is an explicit font: `0` auto (by length: ≤9 chars large, else small),
+  `2` small 5×7, `5` large 10×14. Short positioned text otherwise always
+  renders large, which cannot fit inside a `plasma box`. Encoding is
+  **Latin-1** (one byte = one char, the plasma's wire encoding) — do not send
+  UTF-8 for accented characters. Text coalesces **per position**: a newer
+  queued text replaces an older one at the same `x y` only, so multi-field
+  layouts (callsign + score) can update one field without losing the others.
 - **`plasma row`** — one full bitmap row: `<y>` 0–31 (decimal or `0x` hex),
   then exactly **32 hex digits** = 16 bytes = 128 pixels, **MSB = leftmost**.
   Rows are written strictly in arrival order (unlike `plasma text`, which
-  coalesces to the newest — a bitmap frame is many rows and must not tear);
+  coalesces — a bitmap frame is many rows and must not tear);
   `plasma clear` discards any queued rows/text. Up to 128 commands queue;
   beyond that incoming rows are dropped and counted — pace full-frame pushes
   (a 32-row frame is ~0.77 s of wire time at 9600 baud; stream changed rows,
   as the native games did). See
   [OUTPUT-INTEGRATION.md](OUTPUT-INTEGRATION.md#bitmap-graphics-esc-p).
+- **`plasma box`** — an outlined 1-px box with its interior blanked, in pixel
+  coordinates (`x` 0–127, `y` 0–31, must fit the panel). This is the overlay
+  chrome the original games drew for their rank|score field over the callsign
+  bitmap. The wire's graphics command spans whole bytes horizontally, so the
+  write covers the byte-aligned span containing the box; pixels inside the
+  span but outside the box are cleared — place boxes on 8-px boundaries when
+  that matters. Boxes queue FIFO with rows.
 
 Malformed lines are dropped and counted (first few are logged); they **never**
 cost a client its connection. The endpoint sends no replies.