SolidStart 1.0 server$ RPC Boundaries and Fine-Grained Reactive Tracking

--- description: SolidStart 1.0 server$ RPC Boundaries and Fine-Grained Reactive Tracking - Enforce strict isolation between SolidJS fine-grained client signals and SolidStart 1.0 server$ RPC boundaries. Ensure server functions remain pure serializable RPCs that never capture lexical client scope, with all client-server data synchronization orchestrated strictly through query(), cache(), and createAsync() inside Suspense boundaries. globs: src/**/*.{ts,tsx} alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/solidstart-server-function-async-boundary-integrity" --- # SolidStart 1.0 server$ RPC Boundaries and Fine-Grained Reactive Tracking > **Severity**: CRITICAL | **Category**: frontend > **Anti-Pattern Warning**: Lexical Scope Capture and Manual Effect Fetching Across server$ RPC Boundaries ## System Constraints You are a Principal Engineer enforcing SolidStart 1.0 Server Functions & Async Boundaries. Mandate that server$ closures never capture outer client signals or lexical environment state, payloads remain JSON-serializable, and async reads utilize createAsync and query caching primitives rather than imperative createEffect signal writes. ## Strict Guidelines - Engineers MUST ALWAYS define server$ functions at the module level or ensure they accept strictly serializable arguments (primitives, plain objects) rather than closing over component-scoped signals or props. - Engineers MUST ALWAYS wrap data-fetching server$ calls with query() or cache() from @solidjs/router and consume them via createAsync(() => ...) to establish declarative signal dependencies. - Engineers MUST NOT call server$ directly inside createEffect or createRenderEffect to populate local client signals with fetched data. - Engineers MUST NOT pass non-serializable objects (DOM nodes, functions, class instances with prototypes, reactive Store proxies) as arguments to server$ functions. - Components NEVER render asynchronous resources derived from server$ without an enclosing <Suspense> boundary. - Code SHOULD leverage action() and useAction() from @solidjs/router for state-mutating server$ calls, ensuring automatic cache invalidation and transition safety. ## Bad vs Good Implementations ### Data Fetching with server$ and createAsync #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: server$ closures cannot close over client-side lexical variables (like props or signals). Fetching inside createEffect creates request waterfalls, risks race conditions, circumvents Suspense, and breaks isomorphic server rendering (SSR). ```typescript import { createSignal, createEffect } from "solid-js"; import { server$ } from "@solidjs/start/server"; interface UserData { id: string; name: string; } export default function UserProfile(props: { userId: string }) { const [user, setUser] = createSignal<UserData | null>(null); // ANTI-PATTERN: Capturing component props in server$ lexical scope, // executing RPCs inside createEffect, and manually driving reactive state. const fetchUser = server$(async () => { // Fails in production: props.userId is not available in server runtime context return await db.user.findUnique({ where: { id: props.userId } }); }); createEffect(() => { fetchUser().then((data) => setUser(data)); }); return <div>{user() ? user()!.name : "Loading..."}</div>; } ``` #### Production Standard (Correct) > **Standard**: fetchUser is isolated at module scope with explicit serializable arguments. createAsync tracks the reactive accessor (() => props.userId), coordinates with the <Suspense> boundary during SSR and hydration, and leverages query() cache deduplication. ```typescript import { type Component, Suspense } from "solid-js"; import { query, createAsync } from "@solidjs/router"; import { server$ } from "@solidjs/start/server"; interface UserData { id: string; name: string; } // Module-level RPC function accepting explicit, serializable parameters const fetchUser = query( server$(async (userId: string): Promise<UserData | null> => { "use server"; return await db.user.findUnique({ where: { id: userId } }); }), "users" ); const UserProfile: Component<{ userId: string }> = (props) => { // Declarative fine-grained subscription via createAsync with tracked accessor const user = createAsync(() => fetchUser(props.userId)); return ( <Suspense fallback={<div>Loading user profile...</div>}> <div>{user()?.name}</div> </Suspense> ); }; export default UserProfile; ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: SolidStart 1.0 server$ RPC Boundaries and Fine-Grained Reactive Tracking

SolidStart 1.0 server$ RPC Boundaries and Fine-Grained Reactive Tracking defines an industrial-grade behavioral standard for frontend engineering. Enforce strict isolation between SolidJS fine-grained client signals and SolidStart 1.0 server$ RPC boundaries. Ensure server functions remain pure serializable RPCs that never capture lexical client scope, with all client-server data synchronization orchestrated strictly through query(), cache(), and createAsync() inside Suspense boundaries. Modern software architectures require strict adherence to deterministic patterns to guarantee high availability, maintainability, and zero security vulnerabilities.

Framework Paradigm Shift & Drift MechanicsLLMs are trained on millions of open-source repositories containing outdated code, legacy idioms, and unpatched antipatterns. When coding assistants generate implementations for this stack, they default to common statistical tokens: Lexical Scope Capture and Manual Effect Fetching Across server$ RPC Boundaries Without an explicit system instruction file, developers spend hours debugging silent failures.

Failure Modes & Production Blast Radius

Hazard Analysis: What Breaks Without This Rule

The following failure modes have been cataloged from hundreds of hours of production code reviews where AI assistants produced non-compliant implementations:

Failure Mode	AI Symptom (The Anti-Pattern)	Severity	Production Impact & Remedy
AI Hallucination & Deprecation Drift	Lexical Scope Capture and Manual Effect Fetching Across server$ RPC Boundaries	Critical	Violating this industrial standard introduces regression bugs, security risks, and unexpected runtime failures in production. Enforce explicit behavioral system directives across all AI coding assistants in your repository.
Silent Architecture Inconsistency	AI assistants produce mixed paradigms across files, creating fragmented codebase conventions.	Medium	Increases cognitive load during code reviews and leads to maintenance debt across engineering teams. Pin project conventions in .cursor/rules, CLAUDE.md, and AGENTS.md so all team agents follow identical guardrails.

Architectural Directives in Detail

Step-by-Step Production Directives

Each rule constraint below is injected into the AI agent's system prompt to establish deterministic boundaries:

Engineers MUST ALWAYS define server$ functions at the module level or ensure they accept strictly serializable arguments (primitives, plain objects) rather than closing over component-scoped signals or props.

Engineers MUST ALWAYS define server$ functions at the module level or ensure they accept strictly serializable arguments (primitives, plain objects) rather than closing over component-scoped signals or props.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.