Claude Code System Prompts

Sender display name, normalized by the harness: Unicode control, format, surrogate, and line/paragraph-separator code points stripped (categories Cc/Cf/Cs/Zl/Zp — covers bidi controls, zero-width characters, and tag characters), trimmed, at most 64 code points (+ ellipsis, never splitting a surrogate pair). Sender-asserted display text (the addressable identity is from) — render it as reported speech, but no client-side character sanitization is needed. Absent when the wire is not exactly one harness-formed envelope and on messages from older senders.