plasma: ESC P bitmap rows through the feedback endpoint (plasma row)

PlasmaCommands.GraphicsWrite/GraphicsRow port the display firmware graphics
command (ESC P s y x w h, MSB-left); PlasmaDisplay.RowAsync writes a locked
whole-row update; the line protocol gains `plasma row <y> <hex32>`. The
router plasma slot becomes a bounded FIFO queue: rows stream in order (a
frame must not tear), texts still coalesce to the newest, clear flushes, cap
128 with counted drops. Docs updated; 442 tests.

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

src/RioJoy.Core/Feedback/FeedbackLineParser.cs

@@ -145,7 +145,7 @@ public static class FeedbackLineParser
         string? sub = NextToken(s, ref pos);
         if (sub is null)
         {
-            error = "plasma needs a subcommand (text|clear)";
+            error = "plasma needs a subcommand (text|clear|row)";
             return false;
         }
 
@@ -163,12 +163,82 @@ public static class FeedbackLineParser
             case "text":
                 return TryParsePlasmaText(s, pos, out command, out error);
 
+            case "row":
+                return TryParsePlasmaRow(s, pos, out command, out error);
+
             default:
                 error = $"unknown plasma subcommand '{sub}'";
                 return false;
         }
     }
 
+    // plasma row <y> <32 hex digits>: one full 128-px bitmap row (16 bytes,
+    // MSB = leftmost pixel), matching the native game's whole-row streaming.
+    private static bool TryParsePlasmaRow(
+        string s, int pos, out FeedbackCommand? command, out string? error)
+    {
+        command = null;
+        error = null;
+
+        string? yToken = NextToken(s, ref pos);
+        if (yToken is null || !TryParseNumber(yToken, out int y))
+        {
+            error = "plasma row needs a row number and 32 hex digits";
+            return false;
+        }
+        if (y is < 0 or > 31)
+        {
+            error = $"plasma row {y} out of range (0-31)";
+            return false;
+        }
+
+        string? hex = NextToken(s, ref pos);
+        if (hex is null)
+        {
+            error = "plasma row needs 32 hex digits of row data";
+            return false;
+        }
+        if (NextToken(s, ref pos) is string extra)
+        {
+            error = $"unexpected token '{extra}'";
+            return false;
+        }
+        if (hex.Length != 32)
+        {
+            error = $"plasma row data must be exactly 32 hex digits (16 bytes), got {hex.Length}";
+            return false;
+        }
+
+        var data = new byte[16];
+        for (int i = 0; i < 16; i++)
+        {
+            int hi = HexNibble(hex[i * 2]);
+            int lo = HexNibble(hex[i * 2 + 1]);
+            if (hi < 0 || lo < 0)
+            {
+                error = $"plasma row data has a non-hex character ('{hex[hi < 0 ? i * 2 : i * 2 + 1]}')";
+                return false;
+            }
+            data[i] = (byte)((hi << 4) | lo);
+        }
+
+        command = new FeedbackCommand
+        {
+            Kind = FeedbackCommandKind.PlasmaRow,
+            Y = (byte)y,
+            Data = data,
+        };
+        return true;
+    }
+
+    private static int HexNibble(char c) => c switch
+    {
+        >= '0' and <= '9' => c - '0',
+        >= 'a' and <= 'f' => c - 'a' + 10,
+        >= 'A' and <= 'F' => c - 'A' + 10,
+        _ => -1,
+    };
+
     private static bool TryParsePlasmaText(
         string s, int pos, out FeedbackCommand? command, out string? error)
     {