Honor explicit default_query_exec_mode; no forced simple_protocol

[btipling]

Summary

Postgres/pgx defaults to prepared-statement caching (cache_statement). Transaction-mode poolers (PgBouncer, Supabase pooler on 6543) need default_query_exec_mode=simple_protocol to avoid SQLSTATE 42P05 (prepared statement "stmtcache_*" already exists).

This PR is non-breaking. baton-sql does not inject simple_protocol when the mode is unset. Callers that need pooler-safe behavior set the param explicitly.

Config state	Behavior
default_query_exec_mode unset (no DSN query key, no connect.params key)	Leave URL as-is; pgx uses its default
Explicit value in DSN or connect.params	Honored (simple_protocol, cache_statement, exec, etc.)

Pooler opt-in

connect:
  dsn: "postgres://${HOST}:6543/${DB}"
  params:
    default_query_exec_mode: simple_protocol

Or via DSN: ?default_query_exec_mode=simple_protocol.

Changes

File	Change
pkg/database/database.go	No inject of simple_protocol when unset (removed forced default)
pkg/database/database_test.go	Unset → no mode key; explicit DSN/params preserved; mysql unchanged
README.md	Document pooler opt-in (not forced default)
examples/redshift-test.yml	Restore opt-in caveat for prepared-statement quirks

Tests

go test ./pkg/database/...
go test ./...

Both exit 0.

Context

• Bead: ds-n4f4
• C1 connector-level defaults remain out of scope for baton-sql

Checklist

• Unset postgres DSN does not inject default_query_exec_mode
• Explicit mode in DSN / connect.params still honored
• Tests + README + redshift example updated
• Unit tests green

[github-actions]

Connector PR Review: Honor explicit default_query_exec_mode; no forced simple_protocol

Blocking Issues: 0 | Suggestions: 0 | Threads Resolved: 0
Criteria: Criteria status: loaded .claude/skills/ci-review.md from trusted base 9e81038.
Review mode: incremental since e4c96bf
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Review Summary
The full PR diff was scanned for security and correctness. The new commit f19600e removes the forced simple_protocol injection that existed at the previously-reviewed SHA, so pkg/database/database.go is now net-unchanged from main; the PR only touches tests, README.md, and the redshift example. This addresses the prior concern that force-injecting default_query_exec_mode was a breaking behavior change for existing postgres connectors relying on the pgx cache_statement default; explicit DSN and connect.params values remain honored via the existing params loop, and the new test Test_buildConnectionURL_PostgresQueryExecMode covers unset, explicit, and mysql cases. No new issues found.

Security Issues: None found.

Correctness Issues: None found.

Suggestions: None.

[github-actions]

No blocking issues found.

[github-actions]

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