Claude's memory API stops matching path substrings

Claude's memory-store API requires a new beta header, agent-memory-2026-07-22, per Anthropic's docs.

The loud failure here is easy to catch, since it throws an error before anything ships. The quiet one isn't: it changes what a working query returns, with nothing in the response to flag it.

Combining the new header with the older managed-agents-2026-04-01 header on one request triggers the loud failure, a 400 instead of a merge.

The quiet change is to path_prefix. Say a filter used the prefix 'user' expecting it to catch paths like 'users/123' too. That stops working: the prefix has to end with a slash and match a whole path segment, not a fragment of one.

Listing calls changed too. They return a stable, server-defined order and ignore any order_by or order parameter sent with the request.

The depth parameter shrank too. It only accepts 0, 1, or being left out entirely.

None of this throws an error, not for path_prefix, not for listing order. That's the actual risk: a 400 gets caught in staging, but a quietly different set of memories doesn't get caught anywhere at all. Anyone with a path_prefix filter built on old substring behavior should check it against real path segments before it changes what an agent remembers.