Fix prepared statement and transaction epoch checking

[daniel-garcia]

Summary

Fixes epoch checking for prepared statements and transactions to prevent old connections from being held indefinitely while ensuring transactions complete gracefully.

Changes:

• Added inTx atomic counter to wrappedConn to track transaction state
• Added epoch checking to wrappedStmt methods (Exec, Query, ExecContext, QueryContext)
  • Returns driver.ErrBadConn if connection is old epoch (outside transactions)
  • Skips epoch check if inside transaction (allows tx to complete)
• Updated wrappedRows.Next() to skip epoch check if inside transaction
• Added comprehensive tests for prepared statements and transactions across DSN changes
• Updated README_V3.md with documentation

Behavior:

• Prepared statements: Automatically switch to new DSN via database/sql re-preparation
• Transactions: Stay on old connection until commit/rollback, then new operations use new DSN

Review & Testing Checklist for Human

• CRITICAL: Verify inTx counter increment/decrement logic is correct - check that Begin/BeginTx increment AFTER error check, and Commit/Rollback always decrement even on error
• CRITICAL: Test transactions across DSN changes in a real application with your actual database and workload patterns
• IMPORTANT: Review epoch check logic in wrappedStmt - verify it doesn't break edge cases like prepared statements created inside transactions
• IMPORTANT: Verify test coverage is sufficient - consider edge cases like nested Begin calls (should fail), concurrent transactions, prepared statements with multiple executions
• Run integration tests locally: cd test/integration && go test -v -race -timeout=10m ./...

Recommended test plan:

1. Start application with hotload driver
2. Create prepared statement and execute it
3. Change DSN file
4. Execute prepared statement again - should work with new DSN
5. Start transaction, execute statements, change DSN mid-transaction, complete transaction - should succeed
6. Execute new query after transaction - should use new DSN

Notes

Potential concerns:

• The inTx counter uses atomic operations but the increment/decrement pattern could be fragile if error handling changes in the future
• The prepared statement test shows statements switch to new DSN immediately, suggesting database/sql already handles this via ResetSession(). The epoch check in wrappedStmt is an additional safety net but may be redundant.
• Transaction behavior assumes database/sql doesn't support nested transactions (which is correct, but worth noting)

Test results:

• All integration tests pass with -race flag
• Stress test: 99.8% success rate during rapid DSN changes
• Tests run against libpq, pgx4, and pgx5 drivers

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Session: https://app.devin.ai/sessions/9387a393aa4d4e88971e65d208cb00ea
Requested by: Daniel Garcia (@daniel-garcia)

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[Copilot]

Pull Request Overview

This PR adds comprehensive integration tests for hotload v3 with support for three PostgreSQL drivers (libpq, pgx/v4, pgx/v5). The tests cover basic functionality, DSN reloading, and stress scenarios including concurrency and race detection. Additionally, it removes v2-specific code (transaction tracking, metrics, modtime monitoring) and introduces a new simplified v3 architecture with a Strategy interface and observability package.

Key changes:

• New integration test suite with testcontainers-go for automatic PostgreSQL setup
• Stress tests for concurrent queries, rapid DSN changes, and race detection
• Removal of v2 transaction management, metrics, and modtime monitoring code
• New fsnotify strategy implementation with hash-based change detection

Reviewed Changes

Copilot reviewed 71 out of 73 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
test/integration/*	New integration test suite with driver matrix, reload, and stress tests
transaction.go	Removed v2 transaction tracking and metrics
fsnotify/strategy.go	New v3 fsnotify strategy with hash-based change detection
observability/*	New observability package for v3 metrics and logging
go.mod	Simplified dependencies, removed v2-specific packages

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[Copilot]

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[Copilot]

@daniel-garcia I've opened a new pull request, #65, to work on those changes. Once the pull request is ready, I'll request review from you.