test(lib): cover connection URL parsing + failure classification (42→57 tests)

Extract parseUrl + classify from diagnostics.ts into a pure diagnostics-classify.ts
(diagnostics.ts imports + re-exports the types; behavior unchanged) so the
connection-failure decision tree — the user-facing 'why did connecting fail'
guidance — is unit-testable without react-native/expo. 15 tests: URL parsing
(port defaults, IPv4-vs-hostname, path/query stripping, malformed rejection) and
every classify branch (malformed, ok, tls, no-internet, health-failed, timeout,
server-unreachable incl. the hostname-only MagicDNS hint). typecheck clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/lib/diagnostics-classify.ts

@@ -0,0 +1,84 @@
+// Pure URL parsing + connection-failure classification, extracted from diagnostics.ts
+// so this decision logic (which produces the user-facing "why did connecting fail"
+// guidance) is unit-testable without react-native / expo-clipboard / expo-device.
+
+export type Classification =
+  | "ok"
+  | "malformed-url"
+  | "no-internet"
+  | "server-unreachable"
+  | "health-failed"
+  | "tls-error"
+  | "timeout"
+  | "unknown"
+
+export interface ProbeAttempt {
+  name: string
+  target: string
+  ok: boolean
+  status?: number
+  durationMs: number
+  error?: string
+  errorCause?: string
+}
+
+export interface ParsedUrl {
+  valid: boolean
+  scheme?: string
+  host?: string
+  port?: string
+  isHostname: boolean
+}
+
+// Hermes' built-in URL is incomplete (hostname/port often unreliable), so parse
+// with a regex instead of `new URL`.
+export function parseUrl(url: string): ParsedUrl {
+  const m = url.trim().match(/^(https?):\/\/([^/:?#]+)(?::(\d+))?/i)
+  if (!m) return { valid: false, isHostname: false }
+  const scheme = m[1].toLowerCase()
+  const host = m[2]
+  const port = m[3] || (scheme === "https" ? "443" : "80")
+  const isHostname = !/^\d{1,3}(\.\d{1,3}){3}$/.test(host)
+  return { valid: true, scheme, host, port, isHostname }
+}
+
+export function classify(
+  parsed: ParsedUrl,
+  health: ProbeAttempt,
+  internet: ProbeAttempt,
+  root: ProbeAttempt,
+): { classification: Classification; summary: string } {
+  if (!parsed.valid) {
+    return { classification: "malformed-url", summary: "The server URL could not be parsed. Check for typos or extra characters." }
+  }
+  if (health.ok) {
+    return { classification: "ok", summary: "Health endpoint responded — connection actually works now." }
+  }
+
+  const txt = `${health.error ?? ""} ${health.errorCause ?? ""}`.toLowerCase()
+  const isTls = /ssl|tls|certificate|trust|handshake/.test(txt)
+  const isTimeout = /timeout|timed out/.test(txt)
+
+  if (isTls) {
+    return { classification: "tls-error", summary: "TLS/certificate problem. Try http:// instead of https://, or fix the server certificate." }
+  }
+  if (!internet.ok) {
+    return { classification: "no-internet", summary: "The device has no working internet/network at all (public check also failed). Check Wi-Fi/data and Tailscale (VPN) status." }
+  }
+  // Internet works, server does not.
+  if (root.ok) {
+    return { classification: "health-failed", summary: `Server is reachable but /global/health failed (HTTP ${health.status ?? "error"}). Likely wrong path, auth, or an old server version.` }
+  }
+  if (isTimeout) {
+    return { classification: "timeout", summary: "Connection to the server timed out (dropped, not refused). Likely a firewall, wrong port, or Tailscale ACL blocking the device." }
+  }
+  return {
+    classification: "server-unreachable",
+    summary:
+      `Internet works, but the server at ${parsed.host}:${parsed.port} is unreachable. ` +
+      (parsed.isHostname
+        ? "Hostname may not resolve from this device (MagicDNS off?). Try the raw Tailscale IP. "
+        : "") +
+      "Confirm the opencode server is running, the device is on the same tailnet, and the port is correct.",
+  }
+}