revert: remove /invoke backwards-compat stripping from remote_forward_v0

The stored URL is always the service base (pre-/invoke); /invoke is appended
unconditionally. The backwards-compat stripping logic was unnecessary and
has been reverted to the original single-line form.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: bekossy

sdks/python/agenta/sdk/engines/running/handlers.py

@@ -2275,13 +2275,9 @@ async def remote_forward_v0(
             got=webhook_url,
         ) from exc
 
-    # The stored url is the service base; /invoke is always the invoke surface.
-    # Strip a trailing /invoke first so existing hooks that stored the full
-    # endpoint URL don't get /invoke/invoke after this PR's behaviour change.
-    base_url = webhook_url.rstrip("/")
-    if base_url.endswith("/invoke"):
-        base_url = base_url[: -len("/invoke")]
-    target_url = f"{base_url}/invoke"
+    # The stored url is the service base (pre-/invoke); the invoke surface lives
+    # at /invoke and is always appended.
+    target_url = f"{webhook_url.rstrip('/')}/invoke"
 
     log.info("remote_forward_v0 POST", url=target_url)