docs: note the removed http_sync exports

required_library_error()'s only caller was require_async_session(),
which went with the JMAP extraction, and its tests pinned the exact
wording using "the async JMAP client" as the example - a string naming
something no longer in the tree, in tests that can no longer go red for
a real user.  The helper is kept, since the condition it describes
recurs whenever a component is built on a single library, but the
example is now a hypothetical.  The AsyncSession and
require_async_session removals from caldav.lib.http_sync get the
CHANGELOG line they were missing.

Prompt: look into PR [#711]

Assisted-By: Claude Opus 5 <noreply@anthropic.com>

Author: tobixen

CHANGELOG.md

@@ -24,6 +24,7 @@ The JMAP support was declared experimental in 3.0, hence the changes below are d
 
 ### Changed
 
+* `caldav.lib.http_sync` no longer exports `AsyncSession` or `require_async_session()`.  They existed only for the async JMAP client, which has moved out of this library; `caldav.lib.http_libraries.required_library_error()` is kept, but has no caller in caldav today.
 * `caldav.jmap` no longer carries its own JMAP client implementation.  It's now a thin re-export of calendaring-jmap.
   * Old imports still work, including the submodule paths the 3.3 documentation used: `from caldav.jmap import JMAPClient`, `from caldav.jmap.error import JMAPAuthError`, `caldav.jmap.convert.jscal_to_ical` and so on all resolve to calendaring-jmap's own modules.
   * Importing `caldav.jmap` now emits a `DeprecationWarning`.  Use `from calendaring_jmap import JMAPClient` going forward; the wrapper will be removed in a future release.

tests/test_http_libraries.py

@@ -181,19 +181,26 @@ def test_async_candidates_is_niquests_then_the_httpx_family(self) -> None:
 
 class TestRequiredLibraryMessage:
     """A library that has no fallback needs different wording from "none of
-    them is installed" - the sync stack may well be running on requests."""
+    them is installed" - the sync stack may well be running on requests.
+
+    The helper has no caller in caldav today; its last one was
+    require_async_session(), removed when JMAP moved out into
+    calendaring-jmap.  It is kept because the condition it describes recurs
+    whenever a component is built on one library, and the example below is
+    written as a hypothetical rather than naming something that no longer
+    exists."""
 
     def test_names_the_required_library(self) -> None:
-        message = required_library_error("niquests", "the async JMAP client")
+        message = required_library_error("niquests", "some niquests-only component")
         assert "niquests" in message
-        assert "the async JMAP client" in message
+        assert "some niquests-only component" in message
 
     def test_does_not_claim_nothing_is_installed(self) -> None:
-        message = required_library_error("niquests", "the async JMAP client")
+        message = required_library_error("niquests", "some niquests-only component")
         assert "none of the supported" not in message
 
     def test_still_points_at_the_extra_and_the_docs(self) -> None:
-        message = required_library_error("niquests", "the async JMAP client")
+        message = required_library_error("niquests", "some niquests-only component")
         assert "caldav[niquests]" in message
         assert DOCS_URL in message