appendToPreviousCluster

Appends one grapheme-continuation codepoint to the most recently written printable cell without moving the cursor.

The parser uses this when a host read boundary forced an already complete printable prefix to be published for interactive latency, and a later byte proves that the grapheme continues with a combining mark, variation selector, ZWJ sequence member, or similar continuation. The sink/core owns locating and mutating the previous cell.

Parameters