feat(chat): share a chat by link — anonymous read-only /shared/<token> page, share/unshare

app/core/caching.py

@@ -6,9 +6,10 @@ Two layers, one module:
   append to their asset URLs (``?v=<token>``).
 * **Response middleware** (``CachingMiddleware`` / ``configure_caching``)
   — applies the caching behavior at the transport layer: the known
-  HTML pages (``HTML_PAGES``) are always revalidated (``no-cache``) and
-  their local asset references are rewritten to carry ``?v=<token>``;
-  ``/assets/*`` is
+  HTML pages (``HTML_PAGES``) and the dynamic share page
+  ``/shared/<token>`` (phase 51) are always revalidated (``no-cache``)
+  and their local asset references are rewritten to carry
+  ``?v=<token>``; ``/assets/*`` is
   served ``immutable`` for a year; everything else — all of ``/api/*``,
   including the SSE chat stream — passes through byte-identical.
 
@@ -125,6 +126,11 @@ HTML_PAGES: tuple[str, ...] = (
     "/tuning.html",
     "/git-sources.html",  # phase 35: the admin git sources page
     "/history.html",  # phase 50: the admin saved-chats page
+    # phase 51: the shared page's STATIC path (the static mount serves
+    # shared.html at /shared.html as well as the real route serves the
+    # dynamic /shared/<token> — both must carry the no-cache + ?v=
+    # contract, so the direct URL can never pin stale assets).
+    "/shared.html",
 )
 
 #: Prefix of the versioned static assets (header-only caching; the body is
@@ -194,9 +200,10 @@ class CachingMiddleware(BaseHTTPMiddleware):
 
     * ``/assets/*`` — ``Cache-Control: public, max-age=31536000, immutable``
       (header only — the body is never read).
-    * the known HTML pages (``HTML_PAGES``) — ``Cache-Control: no-cache``,
-      and (for ``text/html`` bodies) every local asset reference gains
-      ``?v=<token>``.
+    * the known HTML pages (``HTML_PAGES``) plus the dynamic share page
+      ``/shared/<token>`` (phase 51, by path prefix) —
+      ``Cache-Control: no-cache``, and (for ``text/html`` bodies) every
+      local asset reference gains ``?v=<token>``.
 
     Everything else — all of ``/api/*`` (including the SSE chat stream) —
     passes through byte-identical: no header changes, the body stream is
@@ -213,7 +220,14 @@ class CachingMiddleware(BaseHTTPMiddleware):
             response.headers["Cache-Control"] = ASSET_CACHE_CONTROL
             return response
 
-        if path not in HTML_PAGES:
+        # Phase 51: the dynamic share page — ``/shared/<token>`` is a
+        # REAL route (not a static file) serving ``shared.html``, so it
+        # joins the known-page contract by path prefix: no-cache +
+        # ``?v=`` asset rewrite. (``/api/shared/<token>`` — the JSON
+        # read — starts with ``/api/`` and passes through below.)
+        is_known_page = path in HTML_PAGES or path.startswith("/shared/")
+
+        if not is_known_page:
             # /api/* (incl. SSE), /favicon.ico, unknown paths: untouched.
             return response