SolidStart 1.0 Server Functions and Async Boundary Reactive Invariants

--- description: SolidStart 1.0 Server Functions and Async Boundary Reactive Invariants - Enforces strict isolation boundaries for SolidStart 1.0 server$ RPC functions by prohibiting lexical capture of client signals and ensuring serializable parameter passing. Mandates the use of createAsync wrapped in Suspense boundaries to maintain fine-grained reactive synchronization across network boundaries without hydration mismatch or memory leaks. 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-guardrail" --- # SolidStart 1.0 Server Functions and Async Boundary Reactive Invariants > **Severity**: CRITICAL | **Category**: frontend > **Anti-Pattern Warning**: Lexically Capturing Client Signals Within server$ Closures and Calling Async RPCs Outside Solid Reactive Primitives ## System Constraints You are a Principal Software Architect enforcing SolidStart 1.0 server function and async boundary safety. Mandate absolute isolation between client reactive execution contexts and server RPC handlers. Prohibit lexical signal captures in server$, enforce createAsync for resource fetching, mandate Suspense/ErrorBoundary wrapping, and ensure all arguments and return values across server$ RPCs are strictly serializable. ## Strict Guidelines - Engineers MUST ALWAYS evaluate client signals in the client scope and pass unwrapped primitive/serializable values as explicit arguments to server$ functions. - Engineers MUST NOT reference or close over client-side signals, stores, or DOM objects inside the lexical scope of a server$ function body. - Code SHOULD wrap read-only server$ queries using createAsync(() => serverFn(accessor())) from @solidjs/router to maintain fine-grained subscription tracking. - Services MUST sanitize, validate, and constrain server$ responses to return only strictly serializable JSON/DTO objects, stripping database internals and sensitive credentials. - Components NEVER execute raw server$ mutations or queries directly inside JSX bodies or untracked lifecycle hooks without action wrappers or createAsync boundaries. ## Bad vs Good Implementations ### server$ RPC Invocation and Reactive Signal Handling #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: The server$ closure attempts to capture and read a client-side reactive signal directly within the server runtime. Vinxi compiler extracts server$ to an isolated HTTP endpoint, stripping client closure variables. Furthermore, invoking fetchUserData directly outside createAsync bypasses Solid's async dependency tracking and causes hydration failure. ```typescript import { createSignal } from "solid-js"; import { server$ } from "@solidjs/start/server"; export default function UserProfile() { const [userId, setUserId] = createSignal("usr_100"); // ANTI-PATTERN: Closing over client signal `userId` inside server$ closure // Causes Vinxi/Nitro compiler extraction failure or runtime serialization crashes const fetchUserData = server$(async () => { const id = userId(); // ILLEGAL: Signal evaluated inside server execution context return await db.user.findUnique({ where: { id } }); }); // ANTI-PATTERN: Calling async RPC directly without createAsync or Suspense const data = fetchUserData(); return <div>{data?.name}</div>; } ``` #### Production Standard (Correct) > **Standard**: The server function accepts an explicit serializable parameter and isolates server-side execution. The client evaluates userId() inside the createAsync accessor, which establishes a fine-grained reactive subscription and automatically refetches when userId changes, properly coordinated via Suspense. ```typescript import { createSignal, Suspense } from "solid-js"; import { createAsync } from "@solidjs/router"; import { server$ } from "@solidjs/start/server"; // INVARIANT: server$ declared with explicit, serializable parameters const fetchUserData = server$(async (id: string) => { "use server"; if (!id || typeof id !== "string") { throw new Error("Invalid user identity"); } const user = await db.user.findUnique({ where: { id }, select: { id: true, name: true, email: true } }); return user; }); export default function UserProfile() { const [userId, setUserId] = createSignal("usr_100"); // INVARIANT: Client signal evaluated in createAsync accessor, passed as parameter const user = createAsync(() => fetchUserData(userId())); return ( <Suspense fallback={<p>Loading profile...</p>}> <div> <h2>{user()?.name}</h2> <button onClick={() => setUserId("usr_101")}>Switch User</button> </div> </Suspense> ); } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: SolidStart 1.0 Server Functions and Async Boundary Reactive Invariants

SolidStart 1.0 Server Functions and Async Boundary Reactive Invariants defines an industrial-grade behavioral standard for frontend engineering. Enforces strict isolation boundaries for SolidStart 1.0 server$ RPC functions by prohibiting lexical capture of client signals and ensuring serializable parameter passing. Mandates the use of createAsync wrapped in Suspense boundaries to maintain fine-grained reactive synchronization across network boundaries without hydration mismatch or memory leaks. 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: Lexically Capturing Client Signals Within server$ Closures and Calling Async RPCs Outside Solid Reactive Primitives 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	Lexically Capturing Client Signals Within server$ Closures and Calling Async RPCs Outside Solid Reactive Primitives	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 evaluate client signals in the client scope and pass unwrapped primitive/serializable values as explicit arguments to server$ functions.

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.