David Reiss 1b2f50bea1 Dynamic partitioning: client side (#9732) ...

## What changed?
Add client-side of dynamic partition scaling: `partitionCache`,
`PartitionCounts`, `StalePartitionCounts` error,
`invokeWithPartitionCounts`.

The intended behavior is:

For partition-aware calls (add+poll tasks), the client caches the
partition count for active task queues, and uses those partition counts
for load balancing (no change to load balancing algorithm yet). The
client sends its cached partition counts to the server in a grpc header,
and receives updated partition counts with the response in a grpc
trailer. If the updated counts are different, it updates its cache it
for subsequent requests. If the server indicates that the client's view
of partition count is stale, it returns a special `StalePartitionCounts`
error and then client makes one immediate retry with the newly received
counts.

With just this PR by itself, the server will never send counts, the
cache will always be empty, and the client will always fall back to
dynamic config for partition counts, so there's no change in behavior
yet.

## Why?
Implement half of dynamic partition scaling.

## How did you test it?
- [ ] built
- [ ] run locally and tested manually
- [ ] covered by existing tests
- [x] added new unit test(s)
- [x] added new functional test(s) ­– tests are in future PRs

2026-04-17 16:54:19 -07:00

..

message.go-helpers.pb.go

Dynamic partitioning: client side (#9732)

2026-04-17 16:54:19 -07:00

message.pb.go

Dynamic partitioning: client side (#9732)

2026-04-17 16:54:19 -07:00