Lazy Skill Invocation Pattern

Description

Per Justacuriousengineer analysis: skills use lazy tool invocation. The first API call carries only skill names. When Claude invokes the Skill tool, it receives the full skill markdown as a tool result, which then persists in conversation context for the remainder of the session. Consequence: skills cost tokens only when invoked, but once invoked their full text stays in context permanently.

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Sources

src-20260423-542f02260352