fix(connect): fix tailnet 'Connection Failed' (pasted-URL double scheme) + surface real error (#1)

* fix(connect): surface real connection error instead of generic dialog

testConnection swallowed the actual fetch error and returned a bare
boolean, so every failure collapsed to the same "Connection Failed"
text. On-device this made tailnet/LAN connect failures impossible to
diagnose (DNS vs timeout vs 401 vs cleartext all looked identical).

- testConnection now returns { ok, error } with the real error message
- add.tsx and [id].tsx dialogs show the error + target URL, plus a
  Tailscale/MagicDNS hint
- IP field keyboard: decimal-pad -> url, so tailnet hostnames can be
  typed (not just pasted)

Verified backend is healthy and reachable over tailnet (health 200,
port 4096 open in packet filter, cleartext present in shipped v0.2.0
APK), so the failure is client-side and was previously unobservable.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* fix(connect): normalize pasted IP/URL to avoid double scheme

Quick-connect blindly did `http://${ip}:${port}`. Pasting a full URL
(e.g. "http://100.108.64.76:4096", as the clipboard auto-paste offers)
produced "http://http://100.108.64.76:4096:4096" -> malformed URL ->
"Network request failed". This is the real tailnet connect failure:
typing a bare IP worked, pasting the displayed URL did not.

buildUrl now strips an existing http(s) scheme, drops any path, and
lifts a trailing :port out of the host field, so pasted full URLs,
host:port, and bare hosts all resolve to a single well-formed URL.

Reproduced and fixed on the Android emulator (paste full URL: fails
before, connects after).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/connection/add.tsx

@@ -34,8 +34,25 @@ export default function AddConnectionScreen() {
 
   const buildUrl = () => {
     if (mode === "advanced") return url.trim()
-    if (!ip.trim()) return ""
-    return `http://${ip.trim()}:${port || "4096"}`
+    const raw = ip.trim()
+    if (!raw) return ""
+    // Be forgiving about pasted values: a full URL, a host:port, or a
+    // host with a trailing path. Extract scheme, host, and port so we
+    // never produce "http://http://host:4096:4096".
+    const schemeMatch = raw.match(/^(https?):\/\//i)
+    const scheme = schemeMatch ? schemeMatch[1].toLowerCase() : "http"
+    let rest = raw.replace(/^https?:\/\//i, "")
+    rest = rest.split("/")[0] // drop any path/query
+    let host = rest
+    let pastedPort = ""
+    const lastColon = rest.lastIndexOf(":")
+    // Only treat trailing ":NNNN" as a port (ignore IPv6 colons / bare host)
+    if (lastColon > -1 && /^\d+$/.test(rest.slice(lastColon + 1))) {
+      host = rest.slice(0, lastColon)
+      pastedPort = rest.slice(lastColon + 1)
+    }
+    const finalPort = pastedPort || port.trim() || "4096"
+    return `${scheme}://${host}:${finalPort}`
   }
 
   const handleQuickConnect = async () => {
@@ -48,7 +65,7 @@ export default function AddConnectionScreen() {
     setIsConnecting(true)
 
     // Test connection first
-    const success = await testConnection(
+    const result = await testConnection(
       {
         id: "",
         name: name || "My Server",
@@ -59,7 +76,7 @@ export default function AddConnectionScreen() {
       password || undefined,
     )
 
-    if (success) {
+    if (result.ok) {
       // Save and go back
       await addConnection(
         {
@@ -76,7 +93,7 @@ export default function AddConnectionScreen() {
       setIsConnecting(false)
       Alert.alert(
         "Connection Failed",
-        "Could not connect to the server.\n\nMake sure:\n1. OpenCode is running: opencode serve --hostname 0.0.0.0\n2. You're on the same WiFi network\n3. The IP address is correct",
+        `Could not connect to ${serverUrl}\n\n${result.error || "Unknown error"}\n\nMake sure:\n1. OpenCode is running: opencode serve --hostname 0.0.0.0\n2. You're on the same network (or Tailscale is connected)\n3. The address is correct (use the IP for tailnet if MagicDNS isn't enabled)`,
         [{ text: "OK" }],
       )
     }
@@ -128,13 +145,13 @@ export default function AddConnectionScreen() {
         <View style={styles.ipRow}>
           <TextInput
             style={[styles.input, styles.ipInput, isDark && styles.inputDark]}
-            placeholder="192.168.1.100"
+            placeholder="192.168.1.100 or my-mac.ts.net"
             placeholderTextColor={isDark ? "#666666" : "#999999"}
             value={ip}
             onChangeText={setIp}
             autoCapitalize="none"
             autoCorrect={false}
-            keyboardType="decimal-pad"
+            keyboardType="url"
           />
           <Text style={[styles.ipColon, isDark && styles.textDark]}>:</Text>
           <TextInput