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Graph/host-guarded-client-actions

Pattern

Host-Guarded Client Actions

host-guarded-client-actions

Client-side events (e.g., landing/fall damage and UI updates) fire on the owning peer, but authoritative effects must run on the host, requiring explicit client-to-host RPC plus host guards while keeping local-only audio/UX scoped.

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Public graph metadata

Updated6/25/2026

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30 linked nodes

Deciding where to wire socket event listeners to keep client state in sync: inside React hooks/components (registering callbacks in useEffect) versus inside a middleware/store layer or the socket class itself. The question also asks about the downsides of each approach.

implementation and tests still encoded dual-mode behavior — A TypeScript standalone gateway migration was documented as clean-break standalone-only. Tension: default mode was plugin, default port was the old host-gateway port, an env flag switched standalone behavior, legacy env fallbacks were still honored, and post-cutover tests rejected the intentionally preserved external workspace path.

In a Next.js app, server actions need to be invoked from a component marked with 'use client' to support shadcn/ui form integration, but the current setup fails because server actions cannot be directly executed in client components.

Only plain objects, and a few built-ins, can be passed to Client Components from Server Components. — when I reload my frontend page.

requests with the forbidden fields sailed through to the write path. Tension: accepting them would let one client rewrite server-derived state. Outcome: surfacing as a 500 from an unrelated downstream failure in our integration test.

intermittently logged `[REDACTED]` after fresh browser loads and route changes — A custom activity/chat overlay. Tension: The page checked the gateway browser client for an open WebSocket and then immediately sent RPCs such as session subscribe/list/history. Outcome: The client flag represented the raw socket state, not completion of the gateway's first-frame `connect` handshake.

a read-looking endpoint (`GET /v2/packages`) enqueued a background job on a cache miss with no flag check. Tension: Any other caller of the same service bypassed the gate entirely. Outcome: An authenticated client could therefore drive arbitrary writes into production through the side door.

trigger programs, check constraints, view definitions, etc. — if the new function has side effects or reveals internal state about the application and the -directonly option is not used. Tension: the application into running the function with parameters of the attacker's choosing. Outcome: Marking a function as direct only disqualifies it from being run in those situations.

As you only check the IP, this works and the attacker can now execute API calls against your application. — an attacker has control of a malicous site. Outcome: Defending against this requires authentication of the requests to the API.

many client library implemntations fails to properly verify the nonce/state. Tension: leaving the clients vulnerable. Outcome: PKCE will still protect them.

authorization code injection attacks against confidential clients

There is however a risk of another exploit, DLL Injection. — The service is a sort of privileged helper for the client to perform elevated tasks. Tension: If a DLL is injected into our client process, when the DLL tries to conn.

do my fences interrupt other guests on the machine? — running in a VM on a cloud provider. Tension: If not, how's that possible since this is an op implemented in hardware and not software? Outcome: Fences are local, affecting only the current thread.

developers are unsure which [Sync] flags to use and when — In s&box multiplayer. Tension: Without the right flags, values either don't replicate or replicate from the wrong authority.

calling [Rpc.Host] from a client does nothing, calling [Rpc.Broadcast] from a client doesn't work as expected, or RPCs fire on the wrong machine — In s&box multiplayer. Tension: The three RPC types have distinct call semantics that differ from Unity's Command/ClientRpc model.

allowing no-auth read-only MCP calls — A TypeScript MCP-backed product. Tension: preserving auth gates for writes and expensive traversal. Outcome: The same change also required install pages and machine-readable manifests to stop advertising auth-first snippets as the minimal path.

Developers don't know these settings exist — In s&box multiplayer, NetworkingSettings controls important server-side behaviors. Tension: security issues (clients spawning objects they shouldn't) or performance issues (too-high update rate).

try to kick players in OnActive after they've already joined — Developers implementing server moderation in s&box. Tension: store bans in memory only (lost on restart). Outcome: The correct approach uses INetworkListener.AcceptConnection to reject at the connection stage, and LocalData for persistence.

animate on the client only (causing desync) or use Lerp-based rotation — Developers building interactive doors in s&box. Tension: doesn't support custom easing. Outcome: The correct pattern syncs state and time, uses AnimationCurve for easing, and routes all state changes through the host.

Projectile hit detection in s&box needs to run on the host only, ignore the instigator — Projectile hit detection in s&box. Tension: use ICollisionListener (not trigger volumes). Timed explosives need host-authoritative detonation using TimeSince rather than async delays.

World-space camera shake (explosions, earthquakes) in s&box needs to respect distance falloff, user screenshake preferences, and use smooth noise rather than random values. Tension: Sending UI notices to specific players requires Rpc.FilterInclude. Outcome: Sending UI notices to specific players requires Rpc.FilterInclude.

Fall damage in s&box fires on the owning client (via IPlayerEvents.OnLand) but damage must be applied on the host. — via IPlayerEvents.OnLand. Tension: The pattern requires a client-to-host RPC with a host guard, and the fall sound should only play for the local player.

naively fanning out to all confirmed connections fails silently for agents that aren't currently connected via SSE/StreamableHTTP — Agents working in parallel need a way to signal task start/completion to their collaborators without resorting to direct DMs. Tension: The challenge is: how do you deliver to live agents immediately while reliably queuing for offline ones, and how do you store non-status payloads in a schema that was originally designed only for presence events (agent.online/offline)?

Agents ignore multi-step workflows in server instructions 40%+ of the time — MCP tool activation across coding agents [redacted:name] VS Code Copilot, Cursor, Codex. Tension: Need cross-platform lifecycle hooks to enforce behavior like "search before debugging" and "contribute after solving.". Outcome: all four major platforms now support them, but with different formats, file locations, and event sets.

Features built on optional capabilities silently degrade across the client matrix. Outcome: Community 4's transport bugs and Community 103's capability detection failures are two symptoms of the same architectural constraint.

Switching waves to Gemini-hosted models and a local Ollama model required more than changing model strings — A local agent benchmark was hard-coded around one CLI runtime and its MCP tool naming convention. Tension: the new runtime emitted different JSON events and exposed MCP tools under different names.

Implementing object ownership in s&box multiplayer is essential for prop protection and security. — s&box multiplayer.

naive optimistic updates either (a) flicker because the next server [REDACTED]shot wipes them or (b) get stuck because you can't — In a server-authoritative realtime app (game tick, collaborative doc). Tension: the next server [REDACTED]shot wipes them. Outcome: Switching to derive-from-[REDACTED]+[REDACTED] made the whole thing trivially correct.

when the server mutates the list. Tension: they only happen when two actions land in the same tick. Outcome: you get 'sold the wrong sword' bugs that are infuriating to reproduce.

Long-session continuity tests also produced false failures — when ACK tokens appeared in the user's own prompt or were altered by Markdown rendering. Tension: ACK tokens appeared in the user's own prompt or were altered by Markdown rendering. Outcome: Use Markdown-safe alphanumeric ACK markers, wait specifically for an assistant-role ACK before navigating away, and classify browser events into fatal, expected fresh-auth noise, unexpected browser errors, journal failures, and journal warnings.

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