[PECOBLR-1383] Add statement execution hooks for telemetry collection

[samikshya-db]

Summary

This stacked PR builds on #320 and adds statement execution hooks to complete end-to-end telemetry collection.

Stack: Part 3 of 3

• Base: [PECOBLR-1143] Implement telemetry Phase 4-5: Export infrastructure and opt-in configuration #319 (PECOBLR-1143 - Phases 4-5)
• Previous: [PECOBLR-1381][PECOBLR-1382] Implement telemetry Phase 6-7: Collection, Aggregation & Driver Integration #320 (PECOBLR-1381-1382 - Phases 6-7)
• This PR: PECOBLR-1383 (Statement execution hooks)

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Changes

Exported Methods for Driver Integration

telemetry/interceptor.go

• ✅ Exported BeforeExecute() - starts metric tracking for a statement
• ✅ Exported AfterExecute() - records metric with timing and error info
• ✅ Exported AddTag() - adds tags to current metric context
• ✅ Exported CompleteStatement() - marks statement complete and flushes

Statement Execution Hooks

connection.go

• ✅ Added hooks to QueryContext():

  • Calls BeforeExecute() with statement ID from operation handle GUID
  • Uses defer to call AfterExecute() and CompleteStatement()

• ✅ Added hooks to ExecContext():

  • Calls BeforeExecute() with statement ID
  • Proper error handling (includes stagingErr)
  • Uses defer to call AfterExecute() and CompleteStatement()

Documentation

telemetry/DESIGN.md

• ✅ Updated Phase 6 to mark as completed
• ✅ Added statement execution hooks to Phase 7 checklist

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Integration Flow

Connection.QueryContext()
    ↓
BeforeExecute(statementID) → creates metricContext with startTime
    ↓
[Statement Execution]
    ↓
AfterExecute(err) → records metric with latency and error
    ↓
CompleteStatement(statementID, failed) → flushes aggregated metrics

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Testing

All tests passing ✅

• ✅ 99 telemetry tests (2.018s)
• ✅ All driver tests (58.576s)
• ✅ No breaking changes
• ✅ Telemetry properly disabled when not configured

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End-to-End Telemetry

With this PR, the telemetry system is fully functional end-to-end:

1. ✅ Collection - Metrics collected from QueryContext/ExecContext
2. ✅ Aggregation - Statement-level aggregation with batching
3. ✅ Circuit Breaker - Protection against failing endpoints
4. ✅ Export - HTTP POST with retry and exponential backoff
5. ✅ Feature Flags - Server-side control with 5-level priority
6. ✅ Resource Management - Per-host clients with reference counting

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Related Issues

• Builds on: [PECOBLR-1381][PECOBLR-1382] Implement telemetry Phase 6-7: Collection, Aggregation & Driver Integration #320 (PECOBLR-1381-1382)
• Implements: PECOBLR-1383 (Statement execution hooks) ✅

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Checklist

• Export interceptor methods for driver use
• Add hooks to QueryContext
• Add hooks to ExecContext
• Update DESIGN.md checklist
• All tests passing
• No breaking changes