SolidStart 1.0 Server RPCs & Fine-Grained Async Boundary Invariants

--- description: SolidStart 1.0 Server RPCs & Fine-Grained Async Boundary Invariants - Enforces strict boundary separation between client-side fine-grained reactivity and SolidStart 1.0 server$ RPC execution. Prohibits lexical closure leakage across the client/server threshold and mandates the use of query/action wrappers with createAsync to preserve Suspense streaming and prevent reactive fetch loops. globs: src/**/*.{ts,tsx} alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/solidstart-server-rpc-reactive-boundaries-standard" --- # SolidStart 1.0 Server RPCs & Fine-Grained Async Boundary Invariants > **Severity**: CRITICAL | **Category**: frontend > **Anti-Pattern Warning**: Closing Over Client Reactive State Inside server$ RPCs and Invoking Uncached RPCs Directly in Reactive Tracking Scopes ## System Constraints You are a Principal Software Architect enforcing SolidStart 1.0 Server Functions and Async Boundary architectural invariants. Mandate absolute isolation between Solid's fine-grained client-side reactive graph and server$ RPC executions. Ensure all data fetching through server functions is properly keyed, cached, and integrated with createAsync, Suspense, and ErrorBoundary primitives. ## Strict Guidelines - Engineers MUST ALWAYS wrap read-only server$ functions using query() or cache() from @solidjs/router and consume them on the client via createAsync(). - Engineers MUST NOT access client signals, DOM references, or browser-only APIs directly within the lexical scope of a server$ function body; all client inputs MUST be passed explicitly as JSON-serializable arguments. - Engineers MUST NOT invoke raw, uncached server$ calls directly inside reactive tracking scopes (e.g., createEffect, createMemo, or naked JSX interpolations) to prevent unbounded execution loops. - Engineers MUST wrap all async data-dependent component trees in <Suspense> and <ErrorBoundary> to prevent hydration mismatches and allow out-of-order streaming. - Code mutating state MUST wrap server$ invocations in action() from @solidjs/router and orchestrate revalidation using revalidate() or submission signals rather than managing local reactive boolean flags. - Components NEVER pass live Signal getters (e.g., () => count()) or non-serializable objects (classes, Symbols, functions) across the server$ boundary. ## Bad vs Good Implementations ### Data Fetching Across the Server/Client Boundary #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: The server$ function closes over client-side lexical variables (props.userId and window.localStorage), which corrupts the compilation boundary and fails during SSR. Invoking the server function inside createEffect bypasses Solid's Suspense streaming architecture, causes layout flicker, and risks infinite re-execution. ```typescript import { createEffect, createSignal } from "solid-js"; import { server$ } from "@solidjs/start/server"; export default function UserProfile(props: { userId: string }) { const [data, setData] = createSignal<any>(null); const clientToken = window.localStorage.getItem("auth_token"); // Fails in SSR // ANTI-PATTERN: Closure leaks client state into server$ context, // and calling uncached server$ inside createEffect triggers hydration sync errors and layout shift. const fetchUser = server$(async () => { // Leaked closure 'props.userId' & 'clientToken' inside server bundle const res = await db.user.findUnique({ where: { id: props.userId, token: clientToken } }); return res; }); createEffect(() => { fetchUser().then((user) => setData(user)); }); return <div>{data() ? data().name : "Loading..."}</div>; } ``` #### Production Standard (Correct) > **Standard**: The server function is wrapped with query() and given an explicit cache key. It accepts explicit serializable primitives rather than capturing lexical client state. The client consumes it via createAsync passing an accessor function, allowing automatic re-fetching when props.userId changes, fully integrated with Suspense and ErrorBoundary streaming. ```typescript import { Suspense, ErrorBoundary } from "solid-js"; import { query, createAsync } from "@solidjs/router"; import { server$ } from "@solidjs/start/server"; import { db } from "~/server/db"; // GOOD: Define RPC at module level with explicit serializable parameters const getUser = query(server$(async (userId: string) => { "use server"; if (!userId) throw new Error("User ID is required"); const user = await db.user.findUnique({ where: { id: userId } }); if (!user) throw new Error("User not found"); return { id: user.id, name: user.name, email: user.email }; }), "getUser"); export default function UserProfile(props: { userId: string }) { // Pass accessor to createAsync to track reactive parameter changes cleanly const user = createAsync(() => getUser(props.userId)); return ( <ErrorBoundary fallback={(err) => <div role="alert">{err.message}</div>}> <Suspense fallback={<div>Loading user profile...</div>}> <div> <h2>{user()?.name}</h2> <p>{user()?.email}</p> </div> </Suspense> </ErrorBoundary> ); } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: SolidStart 1.0 Server RPCs & Fine-Grained Async Boundary Invariants

SolidStart 1.0 Server RPCs & Fine-Grained Async Boundary Invariants defines an industrial-grade behavioral standard for frontend engineering. Enforces strict boundary separation between client-side fine-grained reactivity and SolidStart 1.0 server$ RPC execution. Prohibits lexical closure leakage across the client/server threshold and mandates the use of query/action wrappers with createAsync to preserve Suspense streaming and prevent reactive fetch loops. 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: Closing Over Client Reactive State Inside server$ RPCs and Invoking Uncached RPCs Directly in Reactive Tracking Scopes 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	Closing Over Client Reactive State Inside server$ RPCs and Invoking Uncached RPCs Directly in Reactive Tracking Scopes	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 wrap read-only server$ functions using query() or cache() from @solidjs/router and consume them on the client via createAsync().

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.