refactor(peer): tighten listener-addr handshake invariant

Follow-up hardening for 348a02c, where `listen_addr` was added to Hello and
HelloAck as `Option<SocketAddr>`. Code review surfaced three concrete problems
that the previous commit left open:

1. Cold-start asymmetry. Discovery and the QUIC/mDNS advertiser are spawned
   concurrently. If discovery saw a cached peer advertisement before our own
   advertiser had written `ctx.local_peer_addr`, our outbound Hello carried
   `listen_addr: None`. The receiver's `peer_record_addr` then returned `None`
   and silently dropped the Hello while we still recorded their HelloAck, so
   peer A learned about peer B but B never learned about A until a later
   handshake happened to win the race.

2. Duplicate game-list pipeline. The previous commit added
   `refresh_peer_games`, which post-handshake issued a `ListGames` to fetch
   `peer.games`. The library-sync path (`LibrarySnapshot`) already populates
   the same field. Both could race on first contact and overwrite each other.
   Worse, `refresh_peer_games` was misnamed: a `peer_game_count > 0` guard
   turned it into a fetch-once-then-no-op helper, while
   `handle_library_summary` independently re-triggered a full handshake when
   `previous_count == 0` was observed, producing a redundant ping-pong on
   every first contact.

3. Argument explosion. `perform_handshake_with_peer`, `spawn_library_resync`,
   and `after_peer_library_recorded` had grown to 6-8 individual parameters
   and acquired `#[allow(clippy::too_many_arguments)]` opt-outs. Every caller
   was destructuring the same fields out of `Ctx`/`PeerCtx`.

Changes (all in one commit because they jointly enforce the same invariant:
"a peer is only ever recorded by its listener address, and the local
listener address must exist before we participate in the protocol"):

- `Hello.listen_addr` and `HelloAck.listen_addr` are now `SocketAddr`, not
  `Option<SocketAddr>`. Wire-incompatible, but PROTOCOL_VERSION already moved
  to 3 in 348a02c so no additional version bump is needed.
- `required_listen_addr` reads `ctx.local_peer_addr` and returns an
  `eyre::Result`; `build_hello_from_state` and `build_hello_ack` both call
  it, so an outbound or inbound Hello can no longer be constructed before
  the local QUIC listener is bound. The inbound path maps this into a
  `Response::InternalPeerError` so the remote peer fails cleanly instead of
  seeing a malformed HelloAck.
- `run_peer_discovery` blocks on `wait_for_local_peer_addr` (25 ms poll,
  shutdown-aware) before subscribing to the mDNS browser. This closes the
  cold-start race for outbound handshakes at the source.
- `refresh_peer_games`, `request_game_list_from_peer`, and the
  `previous_count == 0` re-handshake trigger are removed. The post-handshake
  flow now relies solely on `LibrarySummary`/`LibrarySnapshot`/`LibraryDelta`
  for peer-library state; `ListGames` survives only for the
  `request_game_details_*` paths that fetch per-game file descriptions on
  demand.
- New `HandshakeCtx` (with `from_ctx` and `from_peer_ctx` constructors)
  replaces the long argument lists. All `too_many_arguments` allow-attrs in
  `handshake.rs` are gone, and call sites in `handlers.rs`, `discovery.rs`,
  and `stream.rs` collapse to a single clone.
- `handle_library_delta` no longer acquires a read lock on the apply path:
  the `peer_addr` lookup moved into the `else` resync branch where it is
  actually needed.
- `accept_inbound_hello`'s `remote_addr` parameter is renamed to
  `transport_addr`. It is now used only for warn-log formatting, and the
  new name signals that this is the ephemeral QUIC source port, never the
  authoritative listener address that gets recorded.

User-visible effect: on cold start, peers can no longer end up with an
asymmetric view of each other ("A sees B but B never sees A"). First-contact
library sync now does one handshake plus one snapshot/delta exchange instead
of the previous handshake + ListGames + redundant follow-up handshake. The
direct-connect CLI path (`handle_connect_peer_command`) now fails fast with
"local peer listener address is not ready" if invoked before the QUIC server
has bound; this is intentional - the previous behaviour would have sent a
Hello that the receiver had to silently discard.

Test Plan:
- just fmt
- just clippy
- just test (80 peer + 3 cli + 5 tauri tests pass)
- just build
- Manual: bring up `just peer-cli-alpha`/`bravo`/`charlie`, confirm symmetric
  peer discovery and that games show up on every side after one library
  digest cycle, with no duplicated ListGames traffic in trace logs.

Refs: Review feedback on commit 348a02c (listener-address handshake fix).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/lanspread-peer/src/services/discovery.rs

@@ -11,7 +11,7 @@ use crate::{
     context::Ctx,
     events,
     peer_db::PeerId,
-    services::handshake::perform_handshake_with_peer,
+    services::handshake::{HandshakeCtx, perform_handshake_with_peer},
 };
 
 struct MdnsPeerInfo {
@@ -29,6 +29,10 @@ pub async fn run_peer_discovery(
 ) -> eyre::Result<()> {
     log::info!("Starting peer discovery task");
 
+    if !wait_for_local_peer_addr(&ctx).await {
+        return Ok(());
+    }
+
     let service_type = LANSPREAD_SERVICE_TYPE.to_string();
     let (service_tx, mut service_rx) = tokio::sync::mpsc::unbounded_channel();
     let worker_shutdown = ctx.shutdown.clone();
@@ -93,6 +97,19 @@ pub async fn run_peer_discovery(
     }
 }
 
+async fn wait_for_local_peer_addr(ctx: &Ctx) -> bool {
+    loop {
+        if ctx.local_peer_addr.read().await.is_some() {
+            return true;
+        }
+
+        tokio::select! {
+            () = ctx.shutdown.cancelled() => return false,
+            () = tokio::time::sleep(Duration::from_millis(25)) => {}
+        }
+    }
+}
+
 fn parse_mdns_peer(service: &MdnsService) -> MdnsPeerInfo {
     MdnsPeerInfo {
         addr: service.addr,
@@ -161,33 +178,21 @@ async fn handle_discovered_peer(
     }
 
     if upsert.is_new || upsert.addr_changed {
-        spawn_protocol_negotiation(&info, ctx, tx_notify_ui.clone(), peer_id);
+        spawn_protocol_negotiation(&info, ctx, tx_notify_ui, peer_id);
     }
 }
 
 fn spawn_protocol_negotiation(
     info: &MdnsPeerInfo,
     ctx: &Ctx,
-    tx_notify_ui: UnboundedSender<PeerEvent>,
+    tx_notify_ui: &UnboundedSender<PeerEvent>,
     peer_id: PeerId,
 ) {
     let peer_addr = info.addr;
-    let peer_id_arc = ctx.peer_id.clone();
-    let local_peer_addr = ctx.local_peer_addr.clone();
-    let local_library = ctx.local_library.clone();
-    let peer_game_db = ctx.peer_game_db.clone();
+    let handshake_ctx = HandshakeCtx::from_ctx(ctx, tx_notify_ui);
 
     ctx.task_tracker.spawn(async move {
-        if let Err(err) = perform_handshake_with_peer(
-            peer_id_arc,
-            local_peer_addr,
-            local_library,
-            peer_game_db,
-            tx_notify_ui,
-            peer_addr,
-            Some(peer_id),
-        )
-        .await
+        if let Err(err) = perform_handshake_with_peer(handshake_ctx, peer_addr, Some(peer_id)).await
         {
             log::warn!("Failed to negotiate protocol with peer {peer_addr}: {err}");
         }