One-install Dropbox Sign API v3 front door over two bounded domain packs and seven existing e-signature workflows. The suite publishes 73 executable catalog operations covering 68 of 73 unique operations from Dropbox Sign's immutable official OpenAPI at commit 31136f9035133acb5f055a94f24e006857210fdb. This 13-operation compatibility root preserves every prior ID, effective URL, result shape, and single-page bound while dependencies add 60 operations, including five sensitive-read-marked aliases for complete page walks and the nested bulk-job request collection. Five fail-closed exclusions cover two OAuth credential exchanges, two base64-document JSON responses that bypass file isolation, and one mandatory DELETE body the REST transport cannot serialize. Coverage includes accounts, API apps, signing requests, templates, embedded signing and editing, bulk sends, reports, unclaimed drafts, teams, fax lines, fax delivery, and isolated file downloads. The upgrade repairs origin/path composition, stale entity claims, team-member extraction on its full-walk alias, binary file capture, JSON alternatives, and exact integer parsing. API-key credentials remain connection-owned; a manually enrolled OAuth bearer connection can satisfy the same ingredient. Existing workflow reads and writes retain their approval behavior, new sensitive reads are marked sensitive-read, and every new mutation requires approval. No Source is claimed without live field-presence proof.