fix: stop amputating RC suffixes from docs URLs (#23903)

Fixes #23897 (docs link only — naming rename is in #23905)

- Fix version stripping logic in both Go (`codersdk/deployment.go`) and
TypeScript (`site/src/utils/docs.ts`) to preserve `-rc.X` suffixes
instead of amputating them along with `-devel`
- Add `v0.0.0` fallback in the TS frontend to match Go backend behavior
for dev builds
- Add tests covering RC, devel, and plain release version strings

> 🤖 Written by a Coder Agent. Will be reviewed by a human.

site/src/utils/docs.test.ts

@@ -0,0 +1,67 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+describe("defaultDocsUrl", () => {
+	beforeEach(() => {
+		// Reset module-level caches (CACHED_DOCS_URL in docs.ts and
+		// CACHED_BUILD_INFO in buildInfo.ts) by forcing fresh imports.
+		vi.resetModules();
+		// Clean up meta tags from previous tests so each case starts fresh.
+		document.querySelector('meta[property="docs-url"]')?.remove();
+		document.querySelector('meta[property="build-info"]')?.remove();
+	});
+
+	function setBuildInfoVersion(version: string) {
+		const meta = document.createElement("meta");
+		meta.setAttribute("property", "build-info");
+		meta.setAttribute("content", JSON.stringify({ version }));
+		document.head.appendChild(meta);
+	}
+
+	async function getDocsUrl(path: string): Promise<string> {
+		// Dynamic import so we get a fresh module with cleared caches.
+		const { docs } = await import("./docs");
+		return docs(path);
+	}
+
+	it("should preserve RC prerelease and strip build metadata", async () => {
+		setBuildInfoVersion("v2.32.0-rc.1+abc123");
+		const url = await getDocsUrl("/admin/users");
+		expect(url).toBe("https://coder.com/docs/@v2.32.0-rc.1/admin/users");
+	});
+
+	it("should preserve RC prerelease when no build metadata present", async () => {
+		setBuildInfoVersion("v2.32.0-rc.0");
+		const url = await getDocsUrl("/admin/users");
+		expect(url).toBe("https://coder.com/docs/@v2.32.0-rc.0/admin/users");
+	});
+
+	it("should strip devel suffix and build metadata", async () => {
+		setBuildInfoVersion("v2.16.0-devel+683a720");
+		const url = await getDocsUrl("/admin/users");
+		expect(url).toBe("https://coder.com/docs/@v2.16.0/admin/users");
+	});
+
+	it("should strip build metadata from release version", async () => {
+		setBuildInfoVersion("v2.16.0+683a720");
+		const url = await getDocsUrl("/admin/users");
+		expect(url).toBe("https://coder.com/docs/@v2.16.0/admin/users");
+	});
+
+	it("should strip bare devel suffix with no build metadata", async () => {
+		setBuildInfoVersion("v2.32.0-devel");
+		const url = await getDocsUrl("/admin/users");
+		expect(url).toBe("https://coder.com/docs/@v2.32.0/admin/users");
+	});
+
+	it("should use plain release version as-is", async () => {
+		setBuildInfoVersion("v2.16.0");
+		const url = await getDocsUrl("/admin/users");
+		expect(url).toBe("https://coder.com/docs/@v2.16.0/admin/users");
+	});
+
+	it("should produce unversioned URL for v0.0.0 dev builds", async () => {
+		setBuildInfoVersion("v0.0.0-devel+abc123");
+		const url = await getDocsUrl("/admin/users");
+		expect(url).toBe("https://coder.com/docs/admin/users");
+	});
+});

site/src/utils/docs.ts

@@ -8,10 +8,12 @@ function defaultDocsUrl(): string {
 		return docsUrl;
 	}
 
-	// Strip the postfix version info that's not part of the link.
-	const i = version?.match(/[+-]/)?.index ?? -1;
-	if (i >= 0) {
-		version = version.slice(0, i);
+	// Strip build metadata after '+', then remove a '-devel' suffix
+	// if present. Preserve '-rc.X' suffixes so versioned docs links
+	// point at the correct release candidate.
+	version = version.split("+")[0].replace(/-devel$/, "");
+	if (version === "v0.0.0") {
+		return docsUrl;
 	}
 	return `${docsUrl}/@${version}`;
 }