feat(ai): detect expired Claude login and guide re-login

Expired/revoked OAuth logins only fail at request time — auth status
still reports logged in, so the panel previously showed a bare
"exited with error code" message. Classify auth failures in the query
error path (isAuthError on the aiError event) and add strings/styles
for the re-login notice, terminal button and /login hint. API-key
providers keep the existing settings-dialog hint instead.

Author: abose

src-node/claude-code-agent.js

@@ -2132,9 +2132,21 @@ async function _runQuery(requestId, prompt, projectPath, model, signal, locale,
         // transient (network, rate limit), and if the session really is broken
         // the next attempt will surface a fresh error of its own.
 
+        // Expired/revoked OAuth logins only surface at request time — `claude
+        // auth status` still reports loggedIn because the credentials exist,
+        // but the CLI exits non-zero with a /login hint. Flag it so the
+        // panel can offer a re-login action instead of a raw exit-code
+        // error. Custom API-key providers are excluded — their fix is the
+        // settings-dialog hint appended above.
+        const usingApiKey = !!(envOverrides && envOverrides.ANTHROPIC_AUTH_TOKEN);
+        const isAuthError = !usingApiKey &&
+            /run \/login|invalid api key|not logged in|oauth token|revoke|authentication[_ ]?error/i
+                .test(detailedError);
+
         nodeConnector.triggerPeer("aiError", {
             requestId: requestId,
-            error: detailedError
+            error: detailedError,
+            isAuthError: isAuthError
         });
 
         // Always send aiComplete after aiError so the UI exits streaming state

src/nls/root/strings.js

@@ -2648,6 +2648,9 @@ define({
     "AI_CHAT_MODE_INFO_EDIT": "AI can edit files. Shell commands need approval (Click to switch)",
     "AI_CHAT_MODE_INFO_FULL_AUTO": "AI can edit files and run commands without approval (Click to switch)",
     "AI_CHAT_MODE_SWITCH_HINT": "[or Shift+Tab]",
+    "AI_CHAT_AUTH_ERROR_NOTICE": "Claude Code is signed out or your login has expired.",
+    "AI_CHAT_AUTH_ERROR_BTN": "Log in to Claude in Terminal",
+    "AI_CHAT_AUTH_ERROR_HINT": "Type /login in the terminal that opens, then send your message again.",
     "AI_CHAT_MODEL_DEFAULT": "Default",
     "AI_CHAT_MODEL_DEFAULT_DESC_CURRENT": "Currently {0}",
     "AI_CHAT_MODEL_SELECT_TITLE": "Choose the AI model for this chat",

src/styles/Extn-AIChatPanel.less

@@ -239,6 +239,23 @@
     }
 }
 
+/* Auth-error action block: button with its /login hint stacked below —
+   tells the user the one thing to do next at a glance. */
+.ai-auth-error-actions {
+    flex-direction: column;
+    align-items: center;
+    gap: 0;
+}
+
+.ai-auth-error-hint {
+    margin-top: 6px;
+    font-size: @ai-text-meta;
+    color: @project-panel-text-2;
+    text-align: center;
+    white-space: normal;
+    overflow-wrap: break-word;
+}
+
 /* One-time inline notice after switching model mid-conversation.
    Sentence-length status prose: secondary tier (12px), reading line-height,
    left-aligned — meta 11px/centered is for one-line stats, not sentences. */