fix(multiplayer): route host seat mutations to the active lobby backend

[jsdevninja]

Summary

• Route host seatMutate to the server WebSocket when a waiting server lobby is active, instead of always preferring a stale P2P adapter left over from an earlier session.
• Clear P2P/broker state when starting server hosting; close the host WebSocket when starting P2P hosting.
• Keep the pregame lobby open on recoverable server errors while hostingStatus === "waiting" (failed Start shows a toast instead of calling cancelHosting()).
• Add seatMutateAsync and startLobbyWithCurrentPlayers so P2P "Start now" and "Fill with AI & start" run seat mutations in order.
• On the server, only auto-start after seat mutations when seat_state.is_full(), matching manual Start and avoiding spurious starts when start_when_full is enabled.

Fixes #1506

Test plan

• Host a server game (2+ players), fill all seats, click Start game — game starts.
• Trigger a failed start (e.g. lobby not actually full) — toast appears and the host lobby remains open.
• Host P2P, then host a server game without a full reload — Start and Kick affect the server lobby.
• P2P lobby with extra empty seats: Start now removes open seats and starts; Fill with AI works.
• With Start when full enabled, Kick does not auto-start; replacing a player with AI on a full lobby still auto-starts when intended.
• pnpm exec vitest run src/stores/__tests__/multiplayerStore.test.ts passes.

[gemini-code-assist]

Code Review

This pull request refactors multiplayer lobby actions to prevent race conditions during game start. It introduces asynchronous seat mutations (seatMutateAsync) and sequential lobby initialization (startLobbyWithCurrentPlayers), alongside cleaner WebSocket and P2P connection teardown helpers. Feedback focuses on improving state-transition robustness by handling connection loss correctly in seatMutateAsync to avoid misleading P2P errors, and consistently selecting store actions via the React hook in HostControlTile instead of bypassing reactivity with getState().

[gemini-code-assist]

[HIGH] Misleading error message on server-hosted lobby connection loss.
Evidence: client/src/stores/multiplayerStore.ts:1049-1058.
Why it matters: When a server-hosted lobby loses connection, isServerHostingActive returns false, causing the mutation to fall through to P2P handling and throw a confusing "P2P host is not active" error instead of "Host connection is not active".
Suggested fix: Check for activeP2PHostAdapter first, and if absent, verify that hostWs is open before sending the mutation.

      seatMutateAsync: async (mutation) => {
        if (activeP2PHostAdapter) {
          await runP2PSeatMutation(mutation, set);
          return;
        }
        if (!isServerHostingActive(get)) {
          throw new Error("Host connection is not active.");
        }
        hostWs!.send(JSON.stringify({
          type: "SeatMutate",
          data: { mutation },
        }));
      },

References

1. L4. Edge cases: Ensure robust handling of connection loss and other edge cases in multiplayer state transitions. ^(link)

[gemini-code-assist]

[MEDIUM] Inconsistent state access and action dispatching.
Evidence: client/src/components/chrome/HostControlTile.tsx:257-259.
Why it matters: Bypassing the selected store actions and using useMultiplayerStore.getState() directly inside fillWithAiAndStart is inconsistent with the rest of the component, which selects actions like startLobbyWithCurrentPlayers and seatMutate via the hook.
Suggested fix: Select seatMutateAsync and showToast at the top of the component using the useMultiplayerStore hook, and use them directly.

Suggested change

	const startLobbyWithCurrentPlayers = useMultiplayerStore(
	(s) => s.startLobbyWithCurrentPlayers,
	);
	const startLobbyWithCurrentPlayers = useMultiplayerStore(
	(s) => s.startLobbyWithCurrentPlayers,
	);
	const seatMutateAsync = useMultiplayerStore((s) => s.seatMutateAsync);
	const showToast = useMultiplayerStore((s) => s.showToast);

References

1. L5. Idiomatic code: Adhere to consistent and idiomatic React/Zustand state management patterns across the codebase. ^(link)

[gemini-code-assist]

[MEDIUM] Inconsistent state access and action dispatching.
Evidence: client/src/components/chrome/HostControlTile.tsx:327-347.
Why it matters: Bypassing the selected store actions and using useMultiplayerStore.getState() directly inside fillWithAiAndStart is inconsistent with the rest of the component, which selects actions like startLobbyWithCurrentPlayers and seatMutate via the hook.
Suggested fix: Select seatMutateAsync and showToast at the top of the component using the useMultiplayerStore hook, and use them directly.

  const fillWithAiAndStart = () => {
    if (!haveAnyDeck) return;
    void (async () => {
      for (const slot of waitingSeats) {
        const deck = pickRandomAiDeck();
        if (!deck) return;
        await seatMutateAsync({
          type: "SetKind",
          data: {
            seatIndex: slot.playerId,
            kind: { type: "Ai", data: { difficulty: "Medium", deck } },
          },
        });
      }
      await seatMutateAsync({ type: "Start" });
    })().catch((err) => {
      showToast(err instanceof Error ? err.message : String(err));
    });
  };

References

1. L5. Idiomatic code: Adhere to consistent and idiomatic React/Zustand state management patterns across the codebase. ^(link)

[gemini-code-assist]

[MEDIUM] Inconsistent state access and action dispatching.
Evidence: client/src/components/chrome/HostControlTile.tsx:438-444.
Why it matters: Bypassing the selected store actions and using useMultiplayerStore.getState() directly inside fillWithAiAndStart is inconsistent with the rest of the component, which selects actions like startLobbyWithCurrentPlayers and seatMutate via the hook.
Suggested fix: Select seatMutateAsync and showToast at the top of the component using the useMultiplayerStore hook, and use them directly.

Suggested change

	onClick={() => {
	void startLobbyWithCurrentPlayers().catch((err) => {
	useMultiplayerStore.getState().showToast(
	err instanceof Error ? err.message : String(err),
	);
	});
	}}
	onClick={() => {
	void startLobbyWithCurrentPlayers().catch((err) => {
	showToast(err instanceof Error ? err.message : String(err));
	});
	}}

References

1. L5. Idiomatic code: Adhere to consistent and idiomatic React/Zustand state management patterns across the codebase. ^(link)

[matthewevans]

Pushed maintainer review fixes on top of current main.

What changed:

• Addressed Gemini's actionable review feedback without reintroducing the stale-P2P routing bug: server-host sockets still take precedence when active, but a waiting server lobby with no live socket now reports Host connection is not active. instead of falling through to a P2P error.
• Switched HostControlTile async error handling to use selected Zustand actions (seatMutateAsync, showToast) instead of ad-hoc getState() reads in the click paths.
• Added store regression coverage for ordered P2P Start now mutations and the disconnected server-host error path.

Local verification:

• cargo fmt --all
• git diff --check
• pnpm --dir client exec vitest run src/stores/__tests__/multiplayerStore.test.ts
• pnpm --dir client run type-check
• pnpm --dir client exec eslint src/stores/__tests__/multiplayerStore.test.ts src/stores/multiplayerStore.ts src/components/chrome/HostControlTile.tsx

[matthewevans]

Implementation review is clean. The PR now keeps server-host seat mutations routed through the active server socket, reports disconnected server-host state without falling through to P2P, preserves ordered P2P start mutations, and has focused regression coverage plus green CI on head 2097a6e.