* feat!: add MRTR behavior support
* feat: harden SEP-2322 MRTR support
* ci: diff public API only on features common to base and head
cargo public-api builds both revisions with the same feature set, so a
feature introduced (or removed) by a PR broke the build of the other
revision. Restrict the all-features diff to features present in both the
base and head revisions.
`receive()` reads incoming lines with `read_until`, which is not
cancellation-safe, and it is polled inside the service loop's `select!`.
When another branch (e.g. an outgoing response) becomes ready while a
request line is only partially read, the `receive()` future is dropped
and the next call's `self.line_buf.clear()` discards the partial bytes,
so that incoming request is silently lost and never gets a response.
Under many concurrent large responses this intermittently drops requests.
Keep the partially-read bytes in `line_buf` across calls and clear it
only after a whole line has been consumed, so a cancelled read resumes
the same line instead of dropping it. The buffer is cleared (retaining
capacity) rather than reallocated per message.
Adds a regression test that fires 200 concurrent 64 KiB tool responses
over real stdio pipes and asserts no response id goes missing.
This also covers the child-process client transport, which reuses
`AsyncRwTransport`.
