Enforce metric label cardinality budgets at registration and block runaway dimensions

[thlpkee20-wq]

Description

Prometheus is fragile against high-cardinality labels. Add a registration wrapper that requires each metric to declare a cardinality budget and refuses new label combinations that would exceed it.

Requirements and context

• Must be secure, tested, and documented
• Should be efficient and easy to review
• Relevant code: src/metrics.ts, src/metrics/slotMetrics.ts
• Drop or relabel offenders to __overflow__

Suggested execution

• Fork the repo and create a branch
• git checkout -b feat/metric-cardinality-budgets
• Implement changes
  • Wrapper API requiring {name, labels, budget}
  • LRU map of seen label tuples per metric
  • Emit metric_cardinality_overflow_total counter
• Validate security and correctness assumptions

Test and commit

• Run tests
  • npm test
• Cover edge cases
  • Budget set to 0 falls back to no-label aggregation
• Include test output and notes

Example commit message

feat: metric label cardinality budgets

Guidelines

• Minimum 95 percent test coverage
• Clear documentation
• Timeframe: 96 hours

[midenotch]

@midenotch has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

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I would like to work on this

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