feat: add mobile pairing Settings plugin

Cargo.toml

@@ -1,4 +1,4 @@
 [workspace]
-members = ["crates/plugin-manager", "crates/agent-controller", "crates/credential-store", "src-tauri"]
+members = ["crates/pairing", "crates/plugin-manager", "crates/agent-controller", "crates/credential-store", "src-tauri"]
 default-members = ["crates/plugin-manager"]
 resolver = "2"

crates/pairing/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "buzz-pairing"
+version = "0.0.0"
+edition = "2021"
+license = "Apache-2.0"
+description = "Buzz NIP-AB device pairing protocol"
+
+[dependencies]
+nostr = { version = "0.44", features = ["nip44"] }
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+thiserror = "2"
+hex = "0.4"
+rand = "0.10"
+subtle = "2.6"
+zeroize = "1.8"
+percent-encoding = "2.3"
+url = "2"

crates/pairing/README.md

@@ -0,0 +1,26 @@
+# Buzz pairing protocol
+
+Ported from [`block/buzz`](https://github.com/block/buzz/tree/ac0ad7c3004683e5db813492846d787404a2b475/crates/buzz-core/src/pairing),
+PR [#8085](https://github.com/block/buzz/pull/8085), under the repository's
+Apache-2.0 license. The imported protocol and tests preserve the source's
+cryptography, event validation, timeout, replay protection, legacy confirmation,
+and encrypted `desktop-code-v1` capability. Local changes extract the module as its
+own crate, make kind 24134 local, update crate paths in documentation, and format
+with this repository's pinned tools.
+
+This crate has no network or Keychain access. Desktop transport and account
+export are owned by `src-tauri/src/pairing`. Its tests include the exact source
+protocol vectors and code-entry proof regressions. Run `bin/cargo test -p
+buzz-pairing` for unit tests and doctests.
+
+The source QR lifetime differs from upstream: `start_source_lifetime()` resets
+its two-minute clock after desktop transport setup and immediately before the
+visible QR is published. The desktop uses that same deadline for expiry. The
+upstream reference starts the clock at session construction and expires the QR
+at that original deadline; retaining that behavior here would shorten the
+visible-QR contract after slow discovery or subscription. Keep this divergence
+when syncing upstream.
+
+The desktop-code port also fails closed when an oversized rejection cannot be
+serialized: exhausting the guess budget clears the code and aborts before the
+fallible reply construction. A regression covers that boundary.