73962435b6
Replace the Swift secp256k1 wrapper with a small native adapter over Bitcoin Core libsecp256k1. This is an alternative to the wrapper upgrade in [#8381](https://github.com/block/buzz/pull/8381), not an additional change to merge alongside it. The adapter covers the three Nostr operations Buzz needs: x-only public-key derivation, BIP-340 signing, and signature verification. It compiles pinned, unmodified upstream C source through SwiftPM. There is no build plugin, plugin approval script, or underscored Swift import. The app and notification extension use an explicit C module map and header search path. This trades the third-party Swift wrapper for a Buzz-owned adapter and responsibility for updating the vendored C source. Upstream v0.8.0 source, its license, and update provenance are included. The release Xcode pin remains separate in [buzz-releases#110](https://github.com/squareup/buzz-releases/pull/110). ### Validation - Native package tests passed on Xcode 27.0 and 26.5: 96 XCTest tests and 65 Swift Testing tests per toolchain. - Added tests cover the official BIP-340 vectors for 32-byte Nostr messages, invalid secret keys, and malformed input lengths. - Full unsigned Release app and notification extension build passed on exact Xcode 27.0. - Vendored files were compared byte-for-byte with upstream v0.8.0. - Full local `just ci` passed. - [Hosted full unsigned iOS Release build](https://github.com/block/buzz/actions/runs/38924020583/job/117051237094) passed. [Hosted Native Swift validation](https://github.com/block/buzz/actions/runs/38924020583/job/117051237153) passed, including the complete simulator build and native controls/push navigation tests. - Codex code review and security review completed with no findings. ### Before merge - [x] Tom selected the direct-C approach with vendored upstream source; [the wrapper alternative](https://github.com/block/buzz/pull/8381) is closed. Signed-off-by: Tom Brow <tomb@block.xyz>
Native secp256k1
vendor/src, vendor/include, and vendor/COPYING are unmodified files from
Bitcoin Core libsecp256k1 v0.8.0, commit
6e2c8bc4ecdc6e71dbe7a368f360d8d453ce435d:
6e2c8bc4ec
The upstream MIT license is retained in vendor/COPYING. SwiftPM compiles the
three translation units listed in Package.swift, with the extrakeys and
schnorrsig modules enabled. Upstream precomputed tables are checked in; no
build plugin, downloaded binary, or generated source is needed.
To update, replace these three vendor paths from a reviewed upstream release. Do not edit upstream sources locally. Run the NostrSchnorr BIP-340 vector tests, all BuzzPushKit tests, and complete app and notification extension builds on supported Xcode versions before accepting an update.
The BIP-340 test fixture comes from bitcoin/bips commit 927b6de9915c9262615a6399de51b200f81e5aa4, bip-0340/test-vectors.csv.