fix: prevent document link click from resetting active session (#2055)

* fix: prevent document link click from resetting active session

Clicking a #document-<uuid> link in chat caused the session to reset
because of two issues:

1. chatRenderer.js: clicking on the text inside an <a> yields a Text
   node target whose .closest() is undefined, so preventDefault never
   fires and the browser performs a default hash-navigation

2. sessions.js: the hashchange handler treated the entity hash
   (document-<uuid>) as a session lookup, found no match, and the
   subsequent loadSessions created a new default-model chat

Fix: walk past Text nodes before calling .closest(), and skip
entity-prefixed hashes in the hashchange handler.

Fixes #2035

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix(documents): move isOpen=true after container check in openPanel

isOpen was set to true before the #chat-container existence check.
If the container was missing during a race, the function returned
early but isOpen stayed true, preventing the panel from ever
reopening on subsequent calls.

Move isOpen=true to after the container guard so a failed open
doesn't leave the flag stuck.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

static/js/document.js

@@ -3728,6 +3728,9 @@ import * as Modals from './modalManager.js';
       _minimizedDocId = null;
       Modals.unregister('doc-panel');
     }
+    const container = document.getElementById('chat-container');
+    if (!container) return;
+
     isOpen = true;
     // Doc was opened last → it goes in front of the email windows (clears the
     // email-front flag; the doc/email z-index alternation lives in CSS).
@@ -3735,9 +3738,6 @@ import * as Modals from './modalManager.js';
     _ensureAgentMode();
     _markDocVisibleState(_lastSessionId, 'open');
 
-    const container = document.getElementById('chat-container');
-    if (!container) return;
-
     document.body.classList.add('doc-view');
 
     // Sync toggle button state