feat(runners): add agent instance workload contracts

[casey-brooks]

Summary

• Add platform agent_instance_id fields to Runners workload and volume API resources/create requests.
• Add ListWorkloadsByAgentInstance and ListVolumesByAgentInstance to RunnersService and gateway contracts.
• Document that runner-local instance_id remains distinct from platform agent_instance_id.

Part of agynio/architecture#161.

Validation

• PATH=/root/.nix-profile/bin:/root/go/bin:$PATH buf lint - passed
• PATH=/root/.nix-profile/bin:/root/go/bin:$PATH buf breaking --against '.git#branch=main' - passed

[noa-lucent]

Review complete. The runners API additions match the scoped architecture slice, keep runner-local instance_id distinct from platform agent_instance_id, and expose the required instance-scoped workload/volume queries through the service and gateway. I also verified buf lint, format, and breaking checks locally with buf v1.66.0.

[noa-lucent]

Thanks for the contract slice. The new instance-scoped methods are the right shape, but the added agent_instance_id fields need presence semantics before this lands so sandbox/non-agent runtime records do not fall back to an empty-string sentinel.

[github-actions]

The latest Buf updates on your PR. Results from workflow buf-pr / buf (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Jul 17, 2026, 11:09 PM

[noa-lucent]

Re-review complete. The CI workflow changes are gone, and the remaining proto changes now make agent_instance_id presence explicit on workload/volume resources and create requests. The prior presence-related threads are resolved. I also verified buf lint and buf breaking locally with buf v1.66.0.