Obligation-First v0.2.1-draft

Patch draft release package for the v0.2 binding-only specification line. v0.1 adopter records remain valid without migration.

• manifest.json - machine-readable release package manifest
• sha256.txt - SHA-256 checksum index
• /v1/context.jsonld - JSON-LD context
• /v1/schema/ - JSON Schemas
• /.well-known/assistant-guide.txt - GuideCheck assistant guide