feat: Round-trip parity testing framework (DB → YAML → DB)

[Lazialize]

Problem

When a schema is exported from an existing DB via strata export and then used as input for strata generate, diffs are detected even though no actual changes exist. This is caused by information loss during export (type conversions, missing constraints, etc.), and as shown by multiple existing bugs (#23-#28), there is no systematic testing infrastructure to catch these issues.

Proposed Solution

Build a test framework that automatically verifies DB → YAML → DB round-trip fidelity to guarantee export accuracy.

Test Strategy

1. Round-trip test: Schema YAML → DB apply → export → diff detection → verify zero diff
2. Reverse round-trip test: Existing DB → export → generate from that YAML → verify zero diff
3. Cross-dialect test: Apply the same schema to PostgreSQL/MySQL/SQLite and verify export fidelity for each

Test Case Matrix

Test Target	PostgreSQL	MySQL	SQLite
Basic types (INTEGER, VARCHAR, TEXT, etc.)	✓	✓	✓
DECIMAL (precision, scale)	✓	✓	✓
BOOLEAN defaults (true/false)	✓	✓	✓
ENUM types	✓	✓	-
DialectSpecific types	✓	✓	✓
AUTO_INCREMENT / SERIAL	✓	✓	✓
CHECK constraints	✓	✓	✓
FOREIGN KEY (ON DELETE)	✓	✓	✓
UNIQUE constraints	✓	✓	✓
Indexes (normal, unique)	✓	✓	✓
Default values (string, number, expression)	✓	✓	✓
NULL / NOT NULL	✓	✓	✓
Views	✓	✓	✓

Implementation Plan

1. Test helper (src/cli/tests/helpers/roundtrip.rs — new)

   /// Apply schema YAML to DB, export, and verify zero diff
   pub async fn assert_roundtrip_parity(
       schema_yaml: &str,
       dialect: Dialect,
   ) -> Result<()> {
       // 1. Parse schema YAML
       // 2. Generate migration SQL via generate
       // 3. Apply to DB via apply
       // 4. Export to YAML via export
       // 5. Compare original schema with exported schema
       // 6. Assert zero diff
   }

2. Test files (src/cli/tests/)

   • e2e_roundtrip_postgres.rs — PostgreSQL round-trip tests
   • e2e_roundtrip_mysql.rs — MySQL round-trip tests
   • e2e_roundtrip_sqlite.rs — SQLite round-trip tests

3. Test schema templates (src/cli/tests/fixtures/roundtrip/)

   • YAML schema files for each test case
   • Dialect-specific expected value files

4. CI integration: Use testcontainers to automatically run PostgreSQL/MySQL round-trip tests in CI

Existing Bug Regression Coverage

This framework will automate regression tests for the following existing bugs:

• export: PostgreSQL dialect-specific types (INET, CIDR, VARBIT) are converted to TEXT #23: PostgreSQL INET/CIDR/VARBIT → TEXT
• export: CHECK constraints are lost during schema export #24: CHECK constraints lost
• export: MySQL dialect-specific types (TINYINT, SET, MEDIUMINT, YEAR) are lost or misidentified #25: MySQL TINYINT/SET/MEDIUMINT/YEAR lost
• export: MySQL INTEGER columns get spurious precision: 10 added #26: MySQL INTEGER spurious precision
• export: SQLite DOUBLE type is exported as FLOAT #27: SQLite DOUBLE → FLOAT
• export: SQLite auto_increment is lost during schema export #28: SQLite auto_increment lost

Files Affected

• src/cli/tests/helpers/roundtrip.rs (new)
• src/cli/tests/e2e_roundtrip_*.rs (new)
• src/cli/tests/fixtures/roundtrip/ (new)

Alternatives Considered

• Snapshot tests: Save export result snapshots and compare. High maintenance cost when schemas change
• SQL-level comparison: Compare generated SQL directly. Dialect SQL syntax differences are too large; YAML-level comparison is more appropriate

Additional Context

• Corresponds to "Round-trip parity tests (DB → YAML → DB)" in ROADMAP.md
• Can leverage the existing testcontainers infrastructure (testcontainers 0.26, testcontainers-modules 0.14)
• Build on existing E2E test patterns (e2e_*.rs)