Round 11 P2 finding: the stop-sequence chips input rejected any draft
that strip to empty, which silently dropped pasted whitespace stops
like `"\n\n"` for blank-line halts. Local llama-server and OpenAI-
compat backends accept those; the Anthropic helper independently
filters whitespace entries before they hit the wire, so allowing them
in the UI cannot turn into a 400.
Drop the .trim() gate; reject only the truly empty draft. Single-line
Input behaviour is unchanged for the common typed-letters path.
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