NIP-G6: OpenWyrd Capability-URL Inline Rendering

[DeltaClimbs]

TL;DR

Defines a rendering contract for Nostr clients to recognize OpenWyrd MOP capability URLs in kind:1 content (or NIP-17 inner sealed events), fetch the envelope, decrypt client-side using the URL fragment, and render plaintext inline in feed in lieu of the standard OpenGraph card.

Zero sender burden — no tags, no signer changes, no wire-format additions. Senders paste URLs exactly as today; the entire delta is on the rendering client.

Successor to withdrawn NIP-C6

Both review objections from #2327 are baked in:

1. Sender burden → zero. Entire delta on the rendering client.
2. URL self-identification → preserved. Clients pattern-match on URL shape (16-char handle + 43-char base64url key — distinctive enough to skip false-positives). The NIP supplies the protocol-specific decryption knowledge that pattern-matching alone can't.

What the client does

1. Detect URL: https://<host>/w/<handle>#<K_read>
   handle: ^[A-Za-z0-9_-]{16}$    K_read: ^[A-Za-z0-9_-]{43}$ (32 bytes)

2. Fetch:    GET https://<host>/api/v1/wyrds/<handle>
             MOP-Protocol-Version: 1
   Returns:  { handle, envelope, k_origin_pub, published_at, expires_at, replies_enabled }

3. Decrypt:  envelope = 0x01 || iv(12) || ct(N) || tag(16)
             aad      = 0x01 || handle_raw(12) || be8(expires_at_ms) || replies_enabled(1)
             plaintext = AES-256-GCM-Decrypt(K_read, iv, ct||tag, aad)

4. Render:   plaintext + "OpenWyrd MOP" badge + expiry indicator,
             replacing the standard OG card.

Full constants, response shapes, tombstone handling, and BIP-340 attestation verification inlined in G6.md §3 — self-contained, no external links required to implement.

Threat model (no privacy delta)

The capability URL is a bearer secret — posting it publicly already grants read access to every reader. This NIP does not change who can decrypt, only whether the recipient sees plaintext in-feed or has to tap-and-leave. Host read-blindness (K_read never travels HTTP, RFC 3986 §3.5) is unchanged. Clients implementing this NIP MUST NOT transmit K_read to any third party.

Reference implementation

@openwyrd/mop on npm (Apache-2.0). Live test: any https://sendwyrd.com/w/<handle>#<key> URL.

Number

G6 picked after scanning merged NIPs and ~200 open/closed PRs — no conflict. G is outside the hex convention used by merged NIPs to date; happy to renumber per editor preference.