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frontendcritical PriorityID: solidstart-server-function-boundary-serialization

SolidStart 1.0 server$ RPC Boundaries & Fine-Grained Reactive Decoupling

Enforces strict isolation between client-side SolidJS fine-grained reactive scopes and Vinxi-compiled server$ RPC endpoints. Prevents closure state leakage, unhandled async tracking breaks, non-serializable boundary payloads, and SSR hydration mismatches across network edges.

Prohibited Anti-Pattern: Closing over client reactive signals within server$ bodies and invoking async RPCs directly inside synchronous tracking computations.

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---
description: SolidStart 1.0 server$ RPC Boundaries & Fine-Grained Reactive Decoupling - Enforces strict isolation between client-side SolidJS fine-grained reactive scopes and Vinxi-compiled server$ RPC endpoints. Prevents closure state leakage, unhandled async tracking breaks, non-serializable boundary payloads, and SSR hydration mismatches across network edges.
globs: src/**/*.{ts,tsx}
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/solidstart-server-function-boundary-serialization"
---

# SolidStart 1.0 server$ RPC Boundaries & Fine-Grained Reactive Decoupling

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Closing over client reactive signals within server$ bodies and invoking async RPCs directly inside synchronous tracking computations.

## System Constraints
You are a Principal Software Architect enforcing SolidStart 1.0 architectural invariants. Mandate strict boundary isolation for Vinxi server$ functions, preventing illegal signal capture across serialization boundaries and preserving fine-grained reactivity through createAsync and cache primitives.

## Strict Guidelines
- Engineers MUST ALWAYS pass client-side signal values as explicit serializable parameters into server$ RPC functions instead of closing over reactive variables.
- Engineers MUST NEVER access SolidJS reactive primitives (createSignal, useSearchParams, useContext) directly inside the lexical body of a server$ function.
- Engineers MUST ALWAYS wrap server-bound read operations with cache() and query into createAsync(() => ...) accessors to maintain reactive trackability and Suspense integration.
- Engineers MUST wrap mutation server$ functions with action() or useSubmission() primitives to handle revalidation, optimistic updates, and CSRF token propagation.
- Engineers MUST NEVER invoke async server$ functions directly within synchronous tracking scopes (createMemo, createRenderEffect) without going through createAsync or createResource.
- Code SHOULD return JSON-serializable plain primitives, arrays, and POJOs across server$ boundaries; non-serializable instances (Class instances, Symbols, DOM nodes, Functions) are strictly forbidden.
- Components NEVER execute raw Node.js or server-only platform built-ins outside an explicit server$ wrapper or .server.ts file.

## Bad vs Good Implementations
### server$ RPC invocation with signal parameter passing vs reactive closure capture

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Closing over `userId()` inside `server$` attempts to execute client reactivity on the server during the RPC pass. This corrupts code-splitting, leaks client scope into Nitro's server bundle, and fails serialization. Executing `fetchUserData()` directly in JSX returns an unhandled Promise rather than tracking a reactive accessor.
```typescript
import { createSignal, Component } from "solid-js";
import { server$ } from "@solidjs/start/server";
import { db } from "~/server/db";

export const UserProfile: Component = () => {
  const [userId, setUserId] = createSignal("usr_123");

  // CRITICAL BUG: server$ closes over client signal `userId()`.
  // This causes compilation failures, bundle leaking, or stale captures.
  // Additionally, calling raw server$ without createAsync bypasses Suspense.
  const fetchUserData = server$(async () => {
    "use server";
    return await db.user.findUnique({ where: { id: userId() } });
  });

  return <div>{JSON.stringify(fetchUserData())}</div>;
};
```

#### Production Standard (Correct)
> **Standard**: The server function is declared at module scope, accepting an explicit primitive parameter (`id: string`). The client uses `createAsync(() => getUserById(userId()))`, which correctly tracks fine-grained changes to `userId()`, re-triggers the server RPC on change, and coordinates with `<Suspense>` without leaking scope.
```typescript
import { createSignal, Suspense, type Component } from "solid-js";
import { query, createAsync } from "@solidjs/router";
import { server$ } from "@solidjs/start/server";
import { db } from "~/server/db";

// Explicit RPC boundary decoupled from client runtime closures
const getUserById = query(
  server$(async (id: string) => {
    "use server";
    if (!id || typeof id !== "string") {
      throw new Error("Invalid client parameter: id");
    }
    const user = await db.user.findUnique({ where: { id } });
    if (!user) return null;
    
    // Return strictly JSON-serializable DTO
    return { id: user.id, email: user.email, name: user.name };
  }),
  "users"
);

export const UserProfile: Component = () => {
  const [userId, setUserId] = createSignal("usr_123");

  // createAsync tracks the reactive userId() accessor on the client
  // and passes the resolved serializable value over the RPC wire
  const user = createAsync(() => getUserById(userId()));

  return (
    <Suspense fallback={<p>Loading profile...</p>}>
      <div>
        <h1>{user()?.name}</h1>
        <p>{user()?.email}</p>
        <button onClick={() => setUserId("usr_456")}>Switch User</button>
      </div>
    </Suspense>
  );
};
```
Recommended MCP Servers (mcp-serverlist.com)

Equip agent with system tools to verify code for this stack.

Fetch & AST Inspector MCP
Inspects AST boundaries for illegal closure variable bindings across Vinxi compilation entry points.
Recommended Agent Skills (askills.dev)

Ready-to-use executable skill functions tailored to this stack.

SolidStart Vinxi Manifest Analyzer
Validates client/server split bundles and verifies that server$ functions do not bundle client-only runtime artifacts.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: SolidStart 1.0 server$ RPC Boundaries & Fine-Grained Reactive Decoupling

SolidStart 1.0 server$ RPC Boundaries & Fine-Grained Reactive Decoupling defines an industrial-grade behavioral standard for frontend engineering. Enforces strict isolation between client-side SolidJS fine-grained reactive scopes and Vinxi-compiled server$ RPC endpoints. Prevents closure state leakage, unhandled async tracking breaks, non-serializable boundary payloads, and SSR hydration mismatches across network edges. 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 signals within server$ bodies and invoking async RPCs directly inside synchronous tracking computations. 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 ModeAI Symptom (The Anti-Pattern)SeverityProduction Impact & Remedy
AI Hallucination & Deprecation DriftClosing over client reactive signals within server$ bodies and invoking async RPCs directly inside synchronous tracking computations.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 InconsistencyAI 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:

1

Engineers MUST ALWAYS pass client-side signal values as explicit serializable parameters into server$ RPC functions instead of closing over reactive variables.

Engineers MUST ALWAYS pass client-side signal values as explicit serializable parameters into server$ RPC functions instead of closing over reactive variables.

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.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
2

Engineers MUST NEVER access SolidJS reactive primitives (createSignal, useSearchParams, useContext) directly inside the lexical body of a server$ function.

Engineers MUST NEVER access SolidJS reactive primitives (createSignal, useSearchParams, useContext) directly inside the lexical body of a server$ function.

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.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
3

Engineers MUST ALWAYS wrap server-bound read operations with cache() and query into createAsync(() => ...) accessors to maintain reactive trackability and Suspense integration.

Engineers MUST ALWAYS wrap server-bound read operations with cache() and query into createAsync(() => ...) accessors to maintain reactive trackability and Suspense integration.

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.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
4

Engineers MUST wrap mutation server$ functions with action() or useSubmission() primitives to handle revalidation, optimistic updates, and CSRF token propagation.

Engineers MUST wrap mutation server$ functions with action() or useSubmission() primitives to handle revalidation, optimistic updates, and CSRF token propagation.

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.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
5

Engineers MUST NEVER invoke async server$ functions directly within synchronous tracking scopes (createMemo, createRenderEffect) without going through createAsync or createResource.

Engineers MUST NEVER invoke async server$ functions directly within synchronous tracking scopes (createMemo, createRenderEffect) without going through createAsync or createResource.

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.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
6

Code SHOULD return JSON-serializable plain primitives, arrays, and POJOs across server$ boundaries

Code SHOULD return JSON-serializable plain primitives, arrays, and POJOs across server$ boundaries; non-serializable instances (Class instances, Symbols, DOM nodes, Functions) are strictly forbidden.

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.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
7

Components NEVER execute raw Node.js or server-only platform built-ins outside an explicit server$ wrapper or .server.ts file.

Components NEVER execute raw Node.js or server-only platform built-ins outside an explicit server$ wrapper or .server.ts file.

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.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
Technical Questions & Answers

Frequently Asked Technical Questions

Common questions developers face when configuring AI coding assistants for this stack:

Q:Why is SolidStart 1.0 server$ RPC Boundaries & Fine-Grained Reactive Decoupling critical for AI coding assistants?

Enforces strict isolation between client-side SolidJS fine-grained reactive scopes and Vinxi-compiled server$ RPC endpoints. Prevents closure state leakage, unhandled async tracking breaks, non-serializable boundary payloads, and SSR hydration mismatches across network edges. Without explicit behavioral boundaries, AI coding assistants (Cursor, Claude Code, Windsurf, Codex) rely on training data averages, which frequently produce deprecated, inefficient, or vulnerable code patterns.

Q:How does adopting this rule prevent AI hallucinations?

This rule explicitly declares what the AI must avoid (Closing over client reactive signals within server$ bodies and invoking async RPCs directly inside synchronous tracking computations.) and prescribes verified positive examples. Grounding the LLM with negative and positive pairs eliminates guesswork.

Q:Which AI coding environments are supported?

This specification is multi-platform compatible: Cursor (.cursor/rules/*.mdc & .cursorrules), Anthropic Claude Code (CLAUDE.md), Windsurf (.windsurfrules), Codex / Cline (AGENTS.md), and GitHub Copilot (.github/copilot-instructions.md).

Q:Can I combine this rule with other technology stacks?

Yes. Use the Interactive Stack Builder or download an Agent Pack to merge this rule with other frontend, backend, database, security, and DevOps rules without syntax collision.

Open Specification · CC BY 4.0·Free for Personal, Team & Commercial In-Repo Use

Citation & Open Source Attribution Guidelines

This specification is licensed under Creative Commons Attribution 4.0 International (CC BY 4.0). You are completely free to adapt and share this rule in your workspace. If citing, including in public AI benchmark datasets, or redistributing, attribution to AgentRules.org is required.

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