[Snapshot-Agent Memory-Regions 1/N]: Adding proto and feature flag

[Edwinhr716]

What does this PR do?

adds MemoryRegion / MemoryRegionsBackendConfig (oneof field 5, snapshot_name slots) with regenerated Go/Python stubs, server routing to the new backend type, and feature flag.

Why is this change needed?

API-first slice that merges safely alone — a memory-regions request routes to an unregistered backend and fails cleanly until the backend lands

How was this tested?

• Unit tests added/updated
• Integration/e2e tests added/updated
• Manual testing performed

Checklist

• Commits are signed off (git commit -s) per DCO
• Code follows project contributing guidelines
• Tests pass locally (make test)
• Linters pass (make lint)
• Documentation updated (if applicable)

Related Issues

Summary by CodeRabbit

• New Features

  • Added configuration support for selecting device-memory regions by process, address, and size.
  • Added optional snapshot naming for selected memory regions.
  • Added a dedicated memory-regions backend option.

• Bug Fixes

  • Memory-regions configurations are now rejected with a clear precondition error when the feature is disabled.
  • Added independent feature-gate control for memory-regions snapshots.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 7f2fbc2c-8da2-4766-a805-1e7ae40010a2

📥 Commits

Reviewing files that changed from the base of the PR and between 4f9674e and 7b866ad.

⛔ Files ignored due to path filters (1)

• pkg/snapshot-agent/api/v1alpha1/snapshot_agent.pb.go is excluded by !**/*.pb.go

📒 Files selected for processing (7)

• pkg/client/python/timeslice/snapshot_agent/snapshot_agent_pb2.py
• pkg/snapshot-agent/api/v1alpha1/snapshot_agent.proto
• pkg/snapshot-agent/backends/checkpoint.go
• pkg/snapshot-agent/features/features.go
• pkg/snapshot-agent/features/features_internal_test.go
• pkg/snapshot-agent/server/server.go
• pkg/snapshot-agent/server/server_feature_gates_internal_test.go

Included review availability: Your plan provides up to 1 included review per hour; 0 remain after this review.

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📝 Walkthrough

Walkthrough

The snapshot-agent API now supports explicit device-memory regions through BackendConfig.memory_regions. A disabled-by-default MemoryRegionsBackend gate validates this configuration, and the server routes enabled configurations to BackendMemoryRegions.

Changes

Memory regions backend

Layer / File(s)	Summary
Memory regions schema and backend contract pkg/snapshot-agent/api/v1alpha1/snapshot_agent.proto, pkg/client/python/timeslice/snapshot_agent/snapshot_agent_pb2.py, pkg/snapshot-agent/backends/checkpoint.go	Adds MemoryRegion, MemoryRegionsBackendConfig, and the BackendConfig.memory_regions option. Adds the BackendMemoryRegions backend type and updates the generated Python descriptor.
Memory regions feature gate pkg/snapshot-agent/features/features.go, pkg/snapshot-agent/features/features_internal_test.go	Adds MemoryRegionsBackend and registers it as disabled by default. Updates gate string assertions.
Server validation and backend routing pkg/snapshot-agent/server/server.go, pkg/snapshot-agent/server/server_feature_gates_internal_test.go	Rejects gated configurations with FailedPrecondition, routes enabled configurations to BackendMemoryRegions, and tests gate independence and error identifiers.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to 7b866

This PR adds the memory-regions API and routing behind a feature flag without any supported current-head merge-blocking risk; it is merge-ready after normal checks and review.

Sequence Diagram(s)

sequenceDiagram
  participant SnapshotRequest
  participant SnapshotAgentServer
  participant FeatureGates
  participant BackendRouter
  SnapshotRequest->>SnapshotAgentServer: Submit memory_regions configuration
  SnapshotAgentServer->>FeatureGates: Check MemoryRegionsBackend
  FeatureGates-->>SnapshotAgentServer: Enabled or FailedPrecondition
  SnapshotAgentServer->>BackendRouter: Select BackendMemoryRegions

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Possibly related PRs

• llm-d-incubation/llm-d-rl-time-slicing#107: Both extend BackendConfig and server backend routing with a new backend option.
• llm-d-incubation/llm-d-rl-time-slicing#135: Both update the snapshot-agent schema and generated protobuf bindings.
• llm-d-incubation/llm-d-rl-time-slicing#149: Both extend feature-gate enforcement for backend configurations.

Suggested reviewers: aishukamal

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly identifies the snapshot-agent memory-regions change and its proto and feature-flag additions.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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