chore: sync upstream 2026-10-11

[github-actions]

Clean merge of upstream changes. Auto-merge is enabled.

Upstream is 4 commits ahead.

Upstream commits

a54b513e8 Test the MCP probe User-Agent (#2259)
8e4a8a400 Send the default User-Agent on the MCP endpoint probe (#2258)
9fa93c28e Test the default MCP User-Agent (#2255)
6e768da9d Send a default User-Agent on remote MCP requests (#2254)

Diffstat

 8 files changed, 316 insertions(+), 4 deletions(-)