feat(ui): shared header — Sign in/Sign out and New Chat on every page; hide the Sources nav link from anonymous users

tests/unit/test_chat_persistence.py

@@ -10,7 +10,8 @@ Pinned design (PLAN §7.4 note / phase 14):
 * save points: user message on send, brain message on ``done``;
 * every ``localStorage`` access wrapped in try/catch (failure-safe);
 * size budget ~700k chars, oldest dropped first;
-* ``#new-chat-btn`` in the chat header (chat page only), ≥44px, ghost pill.
+* ``#new-chat-btn`` in the shared header bar (chat, sources, viewer —
+  phase 19, owner permission 2026-08-23), ≥44px, ghost pill.
 """
 from __future__ import annotations
 
@@ -144,24 +145,29 @@ def test_new_chat_clears_key_and_ui() -> None:
     assert "removeItem(STORAGE_KEY)" in js
 
 
-def test_new_chat_button_in_chat_header_only() -> None:
-    """#new-chat-btn lives in the chat header (index.html) as a real
-    type=button with an accessible name — and nowhere else (A10: chat-page
-    only control)."""
+def test_new_chat_button_in_the_shared_header_bar() -> None:
+    """#new-chat-btn is a real type=button with an accessible name in the
+    chat header (index.html). Phase 19 (owner permission 2026-08-23): it
+    is part of the SHARED bar — it also appears in sources.html and the
+    document viewer, where it means "go to the chat, fresh" (the
+    clear-storage + navigate binding is pinned in test_shared_header.py)."""
+    for html in (INDEX_HTML, SOURCES_HTML, DOCUMENT_HTML):
+        text = html.read_text(encoding="utf-8")
+        btn = re.search(r'<button[^>]*id="new-chat-btn"[^>]*>', text)
+        assert btn, f"{html.name} must contain #new-chat-btn"
+        tag = btn.group(0)
+        assert 'type="button"' in tag
+        assert 'aria-label="New chat"' in tag
+    # Chat page specifics: the button sits after the nav, inside the header.
     html = _index()
     btn = re.search(r'<button[^>]*id="new-chat-btn"[^>]*>', html)
     assert btn, "index.html must contain #new-chat-btn"
-    tag = btn.group(0)
-    assert 'type="button"' in tag
-    assert 'aria-label="New chat"' in tag
     nav_idx = html.find('<nav class="app-nav"')
     assert nav_idx != -1 and btn.start() > nav_idx, (
         "the button belongs after the nav, inside .header-inner"
     )
     main_idx = html.find('main id="main"')
     assert main_idx != -1 and btn.start() < main_idx, "the button belongs in the header"
-    assert 'id="new-chat-btn"' not in SOURCES_HTML.read_text(encoding="utf-8")
-    assert 'id="new-chat-btn"' not in DOCUMENT_HTML.read_text(encoding="utf-8")
 
 
 def test_new_chat_button_style_contract() -> None: