Add Network discovery metadata

[rchatham]

Summary

Adds Bonjour discovery identity metadata for the Network transport stack so discovered Network browser results can map to framework-neutral PeerIdentity values and endpoints.

Changes

• Add PeerNetworkDiscoveryInfo for TXT record encode/decode.
• Validate discovery metadata:
  • required identifier/display name/protocol version
  • supported protocol version only
  • non-empty values
  • bounded TXT-record-safe advertised lengths
• Advertise local peer discovery metadata from NetworkPeerListener.
• Parse NWBrowser.Result Bonjour metadata in NetworkPeerBrowserTransport.
• Store PeerIdentity -> NWEndpoint mappings for later invitePeer connection attempts.
• Ignore self-discovery in the browser adapter.
• Keep malformed/missing metadata ignored.

Non-goals

• No public backend selector yet.
• No default backend change.
• No trust/auth claim for TXT metadata; it is discovery routing data only.
• No local simulator loopback integration yet.

Verification

• swift test — 88 tests passed
• xcodebuild test -project PeerConnectivity.xcodeproj -scheme PeerConnectivity -destination 'platform=iOS Simulator,name=iPhone 16,OS=18.3.1' -configuration Debug — 88 tests passed

Stack context

Stacked on PR #27 (feature/network-migration-transport-adapters). This is the discovery metadata slice in the Network migration stack.

[Copilot]

Pull request overview

Adds Bonjour TXT-record discovery metadata to the internal Network transport so NWBrowser results can be mapped to stable, framework-neutral PeerIdentity values and later resolved back to NWEndpoint for connection attempts.

Changes:

• Introduces PeerNetworkDiscoveryInfo to encode/decode identity + protocol version into Bonjour TXT records.
• Advertises local discovery metadata from NetworkPeerListener and parses it in NetworkPeerBrowserTransport.
• Adds/updates XCTest coverage for discovery TXT record behavior and browser adapter behavior (including self-discovery ignore).

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
Sources/PeerNetworkProtocol.swift	Adds PeerNetworkDiscoveryInfo TXT record encode/decode and validation logic.
Sources/NetworkPeerTransportAdapters.swift	Parses Bonjour metadata from NWBrowser.Result, ignores self results, and maps PeerIdentity to NWEndpoint for invitePeer.
Sources/NetworkPeerTransport.swift	Advertises discovery TXT record via NWListener.Service(..., txtRecord:) when identity is provided.
PeerConnectivityTests/PeerNetworkProtocolTests.swift	Adds round-trip / validation tests for discovery TXT records.
PeerConnectivityTests/NetworkPeerTransportAdapterTests.swift	Updates browser transport tests to use explicit identities and adds self-ignore coverage.

Suppressed comments (1)

Sources/PeerNetworkProtocol.swift:65

• Discovery TXT record validation currently checks String.count for identifier/displayName length. Since the advertised values are constrained in UTF-8 bytes, the validation should also use utf8.count to avoid accepting values that will exceed DNS-SD TXT byte limits (especially for non-ASCII display names).

            protocolVersion == PeerNetworkHandshake.currentProtocolVersion,
            !identifier.isEmpty,
            !displayName.isEmpty,
            identifier.count <= PeerNetworkDiscoveryInfo.maxIdentifierLength,
            displayName.count <= PeerNetworkDiscoveryInfo.maxDisplayNameLength else { return nil }

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[rchatham]

Superseded by consolidated PR #29. No commits were discarded; this branch is preserved as a recovery and reference point. Addressed review findings were replied to and resolved before consolidation.