fix: open #document deep-links on refresh and surface load errors (#631)

Add a hashchange handler for #document-<id> so refresh / URL-bar nav opens the document, and replace the silent console.error in loadDocument with a user-facing toast.

Closes #560

static/js/document.js

@@ -152,6 +152,8 @@ import * as Modals from './modalManager.js';
       addDocToTabs,
       syncDocIndicator: _syncDocIndicator,
     });
+    _maybeOpenDocFromHash();
+    window.addEventListener('hashchange', _maybeOpenDocFromHash);
   }
 
   /** Update overflow-doc-btn accent indicator, toolbar indicator, and session list icon */
@@ -5811,16 +5813,31 @@ import * as Modals from './modalManager.js';
     }
     try {
       const res = await fetch(`${API_BASE}/api/document/${docId}`);
-      if (!res.ok) throw new Error('Not found');
+      if (!res.ok) throw new Error(res.status === 404 ? 'Not found' : `HTTP ${res.status}`);
       const doc = await res.json();
       addDocToTabs(doc, doc.session_id);
       _ensureDocPaneMounted();
       switchToDoc(doc.id);
     } catch (e) {
       console.error('Failed to load document:', e);
+      if (uiModule) {
+        const msg = e.message === 'Not found'
+          ? 'Document not found — try opening it from the Library.'
+          : 'Could not open document.';
+        uiModule.showError(msg);
+      }
     }
   }
 
+  // Deep-link: #document-<id> opens that document on load / URL-bar nav.
+  // Clicks on in-chat document anchors are handled separately (they call
+  // preventDefault, so they don't change the hash); this covers refresh
+  // and pasted/typed document URLs, which previously did nothing.
+  function _maybeOpenDocFromHash() {
+    const m = (window.location.hash || '').match(/^#document-(.+)$/);
+    if (m) loadDocument(m[1]);
+  }
+
   /** Open panel and ensure a document exists, creating a session if needed */
   export async function ensureDocPanel() {
     let sessionId = _lastSessionId

tests/test_document_deeplink.py

@@ -0,0 +1,33 @@
+"""Regression guards for in-chat document deep-links (#document-<id>).
+
+The frontend module is browser-coupled (window/fetch/document) so there's
+no JS unit harness for it — these pin the source-level invariants that the
+404-silent-failure fix depends on. See issue #560.
+"""
+
+from pathlib import Path
+
+_REPO = Path(__file__).resolve().parents[1]
+
+
+def test_chat_document_links_use_the_document_id():
+    """The list/open tool must anchor to the real document id, not a slug —
+    a slug 404s against the UUID-keyed /api/document/<id> route."""
+    src = (_REPO / "src" / "tool_implementations.py").read_text(encoding="utf-8")
+    assert "(#document-{d.id})" in src
+    assert "(#document-{doc.id})" in src
+
+
+def test_document_deeplink_handled_on_hashchange_and_load():
+    """#document-<id> in the URL must open the doc on refresh / URL-bar nav,
+    not just on click."""
+    js = (_REPO / "static" / "js" / "document.js").read_text(encoding="utf-8")
+    assert "addEventListener('hashchange', _maybeOpenDocFromHash)" in js
+    assert "#document-" in js
+
+
+def test_failed_document_load_surfaces_user_error():
+    """A missing/failed document must tell the user, not fail silently."""
+    js = (_REPO / "static" / "js" / "document.js").read_text(encoding="utf-8")
+    assert "uiModule.showError" in js
+    assert "Document not found" in js