Simple queries are still prepared when setting search_path

Hey,

while building a tool for managing a multi-tenant database I've found behaviour that doesn't seem intended. It can be triggered by this minimal reproduction:

const postgres = require("postgres");

const sql = postgres(null, {
	host: "localhost",
	port: 5432,
	user: "postgres",
	password: "VUYmFyBt8FHZ4Sr3EdFcWSMc",
	database: "firatcms",
	prepare: false,
	connection: {
		// search_path: "project_aq940fcg89", // Commenting in this line breaks
	},
});

const run = async () => {
	// await sql`SET search_path TO project_aq940fcg89;`; // Commenting in this line breaks
	await sql`	CREATE TABLE IF NOT EXISTS "abc" (
		"id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
		"version" int NOT NULL
	);
	ALTER TABLE "abc" DROP CONSTRAINT IF EXISTS "version_unique";
	ALTER TABLE "abc" ADD CONSTRAINT "version_unique" UNIQUE ("version");`.simple();
};

run().then(() => {
	sql.end();
});

The main issue is that I have a query with multiple statements in there and I'd expect it to be not prepared. Firstly because I set prepare: false but also because I added .simple(). In the real code, I use sql.unsafe without a second arg and I checked there that the produced query always has simple: true which is correct as it's based on whether I pass in arguments or not.

After trying it out a bit more, I've found that this issue only occurs when I have a search path set either via the connection or via SET search_path

I tried debugging it myself for an hour now but it's probably some Postgres internals that I don't understand good enough

Start with the minimal JavaScript reproduction in the issue, comparing prepare: false and .simple() with search_path set through connection or SET search_path. Trace the query handling and PostgreSQL behavior for this combination; done means the multi-statement query remains unprepared in both search_path cases, with regression coverage for the reported reproduction.