* fix(outbound): report delivery status in best-effort message send results
Best-effort sends (forced on for implicit message_tool_only source
replies) previously collapsed failed and partial_failed durable send
results into a success-shaped MessageSendResult, so agents saw a
normal-looking envelope while delivery had actually failed. Surface
deliveryStatus, a formatted error, sentBeforeError, and per-payload
outcomes without changing throw semantics.
* fix(outbound): centralize message delivery outcomes
Co-authored-by: masatohoshino <g515hoshino@gmail.com>
* docs(changelog): split aggregate entries from code landing
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Co-authored-by: Peter Steinberger <steipete@gmail.com>
