import_sstpb: add RestoreRegion RPC for snapshot restore

[RidRisR]

What changed and how does it work?

Add ImportSST.RestoreRegion so BR can ask a target Region leader to restore snapshot SSTs through the cloud storage engine. The response reuses IngestResponse; success means the generated files have been applied. Failed or interrupted requests may already have taken effect, so the API does not promise idempotent retries.

RestoreRegionRequest carries the Region context, shared source storage and optional cipher configuration. Each RestoreRegionSource identifies a source write/default SST, its size, logical key-prefix/timestamp rewrite rule and optional IV. TiKV derives the crop range from the target Region. Timestamp filtering is unsupported.

This is an additive protocol change. Existing RPCs and the backup metadata format are unchanged. Include regenerated Go bindings and the compatibility lock; Rust bindings are generated at build time.

Validation

• make proto-fmt-check
• protolock status against both the updated lock and the upstream master lock
• Regenerated import_sstpb using the repository's generation options; git diff --exit-code remained clean
• go test ./pkg/import_sstpb (package compilation; no test files)
• go build ./pkg/...
• cargo check --locked -j 8
• cargo check --locked --no-default-features --features prost-codec -j 8
• git diff --check origin/master...HEAD

The protocol source is byte-for-byte identical to the version used by both BR and TiKV in a prior end-to-end full-snapshot restore test (write/default CFs, secondary index, checksum and three-replica Apply). That test used local dependency overrides on older dependency baselines; integration after updating consumers to this PR revision remains separate work.

C++ generation/build and a new end-to-end consumer run on this rebased revision were not run locally.

Summary by CodeRabbit

• New Features
  • Added support for restoring a complete snapshot into an existing region.
  • Added configuration for target-region context, shared storage, source SST files, column families, rewrite rules, file lengths, and encryption settings.

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between f9b4ae7 and d51dc40.

⛔ Files ignored due to path filters (2)

• pkg/import_sstpb/import_sstpb.pb.go is excluded by !**/*.pb.go
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• proto/import_sstpb.proto

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📝 Walkthrough

Walkthrough

The import SST protocol adds RestoreRegion and request messages for restoring snapshot SST files into an existing region, including storage, column family, rewrite, file-length, and encryption metadata.

Changes

Region Restore

Layer / File(s)	Summary
Restore RPC and request contract proto/import_sstpb.proto	Adds the RestoreRegion RPC, RestoreRegionRequest, and RestoreRegionSource with region context, storage configuration, SST metadata, rewrite rules, and encryption settings.

Estimated code review effort: 3 (Moderate) | ~15–30 minutes

Merge Risk: ⚪ Minimal · up to d51dc

This change adds the RestoreRegion RPC and its SST restore request metadata. The generated bindings align with the new contract, and no concrete current-head merge risk remains.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely identifies the main change: adding the RestoreRegion RPC to import_sstpb for snapshot restoration.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
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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