cl/sentinel: reject invalid ping and status requests

[domiwei]

Summary

• decode Ping/1, Status/1, and Status/2 request bodies before returning success
• return InvalidRequest for empty, truncated, oversized, malformed, and observably trailing requests
• enforce fixed SSZ sizes and bounded Snappy input; Status/2 uses the 92-byte Fulu schema
• update request lifecycle tests to close the write side and clean up handler contexts

Closes #23166.

Testing

• go test ./cl/sentinel/communication/ssz_snappy ./cl/sentinel/handlers ./cl/sentinel -count=1
• GOLANGCI_LINT_CACHE=/private/tmp/issue23166-golangci-cache make lint

[awskii]

Four files here also change in #23577 — ssz_snappy/encoding.go, handlers/heartbeats.go, handlers/rate_limiter_integration_test.go, sentinel_requests_test.go — and its encoding.go edits land in the same functions this PR rewrites. Whichever merges second rebases onto the other.

[Copilot]

Pull request overview

Rejects malformed Ping and Status requests in Caplin’s SSZ-Snappy handlers.

Changes:

• Adds fixed-size request decoding and invalid-request responses.
• Bounds compressed input and checks trailing data.
• Expands handler and lifecycle tests.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
cl/sentinel/sentinel_requests_test.go	Closes request writes before reading responses.
cl/sentinel/handlers/rate_limiter_integration_test.go	Sends valid Ping requests in rate-limit tests.
cl/sentinel/handlers/heartbeats.go	Validates Ping and Status request bodies.
cl/sentinel/handlers/heartbeats_test.go	Tests valid and malformed requests.
cl/sentinel/communication/ssz_snappy/encoding.go	Adds exact-size, bounded decoding.
cl/sentinel/communication/ssz_snappy/encoding_test.go	Tests compressed limits and trailing frames.

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[yperbasis]

Two protocol-boundary issues remain in the exact SSZ-Snappy decoder.

[Copilot]

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