Copies the source session's authored content (description, agenda sections + leader prompts + visuals, participant pre-session work

• reflection prompts) into the response for the target editor's draft state. The agenda fields are NOT persisted to the target until the editor's normal Save (AC-S1); only the slide deck is persisted server-side at this point (AC-CB2 — S3 copy → new session_content_files row for the target, replacing any existing target slide_deck row atomically).

The response applies the TARGET cohort's commitment-tracking gate (AC-CB6): per-section commitment toggles and the pre-session work commitment_review_enabled flag are forced to false when the target cohort has tracking off, so the editor never inherits a stranded value it cannot surface.

The source can live in a different cohort. Both source and target must resolve to a (cohort, modality='group_coaching', session_number) triple — sessions without a session_number or whose cohort lacks an active group_coaching modality return 404.