Import a marketplace item you're ENTITLED to into your PRIVATE library as a launchable base copy, tagged with where it came from (acquired_from). This is the bridge: a bought/imported session lives in the SELLER'S tenant and isn't launchable via the library; acquiring stages a private copy in YOUR personal tenant so a4sx launch --a4sx-session and the lineage tree work on it normally.

Accepts a marketplace COLLECTION (its session member is copied) or a bare SESSION listing (synthesised as a one-member collection below, so the copy, scrub and provenance are identical). Reuses the same cross-tenant read + entitlement gate as GET /memory/collections/{cid}/bundle: the entitlement check is MANDATORY (a paid item without entitlement → 402). Idempotent: re-acquiring the same source stages a NEW VERSION of the same col-lib-* entry.

A collection with NO session member is reading material, not a base → 409 memory_only with the two routes that DO serve it (never a silent no-op: the Library lists only what lands here).

The copy carries a private acquired_from provenance field only — NOT a royalty edge. Publishing a derivative for cross-author credit is the separate, author-gated marketplace builds_on declaration. AUTH: your ge_sess_ session bearer (a human account — the copy lands in your personal library).