{"ok":true,"kind":"lesson","integrity":{"knowledge":"free","capability":"paid_x402_optional","rule":"Every concept on a path is fully teachable without purchase. Skills are optional implementations, never required reading.","display":"Learn free. Buy only if you want a ready-to-run sealed pack."},"lesson":{"schema_version":"lvl-knowledge-lesson-v1","id":"path-x402-04-sealed-pack-integrity","category":"path","path_ids":["build-first-x402-service"],"title":"Sealed packs and integrity checks","summary":"Payment proves you paid. Hash checks prove the files match the listing claim.","body":"## Two different proofs\n\n1. **Payment verification** — chain says USDC arrived  \n2. **Content integrity** — delivered files match published `data_hash`  \n\nNeither replaces the other.\n\n## Conceptual flow\n\n1. Note listing hash (ERC-7857 style metadata)  \n2. Unlock sealed files  \n3. Canonicalize + hash  \n4. Compare; quarantine on mismatch  \n\n## What integrity does not mean\n\nA matching hash does not mean the skill is useful, safe, or continuously monitored. It means **package integrity at seal time**.\n\n## Takeaway\n\nAgents should verify content, not only payment receipts.","concepts":["erc-7857","data-hash","sealed-pack"],"related_skills_optional":[{"skill_id":"sealed-payload-integrity-checker","name":"Sealed Payload Integrity Checker","price_usd":3.99,"price_label":"$3.99 / unlock","summary":"Verify data_hash matches delivered sealed content before trusting an unlock.","outline":"https://lvlltd.com/skills/sealed-payload-integrity-checker/outline.json","challenge":"https://lvlltd.com/api/pay?skill=sealed-payload-integrity-checker","listing":"https://lvlltd.com/listings/sealed-payload-integrity-checker/","available":true,"optional":true,"label":"optional_implementation"}],"sort_order":40,"estimated_minutes":8,"last_updated":"2026-07-22T12:00:00.000Z","freshness":{"last_updated_at":"2026-07-22T12:00:00.000Z","days_since_update":0,"band":"fresh","score_0_100":95,"label":"Fresh","display":"Fresh · updated 2026-07-22 (0d ago)"},"integrity":{"knowledge_free":true,"skills_optional":true,"note":"This lesson is complete without purchasing any skill."},"related_bundles_optional":[],"url":"https://lvlltd.com/learn/lessons/path-x402-04-sealed-pack-integrity/","updated_at":"2026-07-22T21:10:40.587Z"},"note":"Knowledge free. related_skills_optional are implementations, not requirements."}