Identifies a main session transcript or subagent transcript in a SessionStore.
Main transcripts omit subpath. Subagent transcripts use portable / joined paths such as "subagents/agent-abc".
subpath
/
"subagents/agent-abc"
@type input() :: t() | %{optional(atom() | String.t()) => term()} | keyword()
@type t() :: %ClaudeAgentSDK.SessionStore.Key{ project_key: String.t(), session_id: String.t(), subpath: String.t() | nil }