Add Postgres schema definitions and migrations

[Makisuo]

Why

Schema-as-code and migrations (/schema, /kit, /migrate) only supported ClickHouse. The query builder already goes through a Dialect, but the schema layer was written directly against ClickHouse:

• MergeTree engine, orderBy and TTL in the entities
• dialect: "clickhouse" hard-coded in the snapshot
• ReplacingMergeTree ledger tables
• drift checks via system.tables

That blocked Maple from replacing drizzle-kit for its Postgres schema.

What changed

Dialect seam. The snapshot envelope, entity keys and hashing, the branch graph, folder loading and MigrationDriver stay shared. Each dialect now owns its own entities, definitions, diff, ops/DDL, ledger and drift check. generate, run, status and verify choose the dialect from the config or the snapshots. ClickHouse behaviour is unchanged.

Postgres

• Definitions: S.pg.table, with S.pg.column (default, defaultExpr, identity), S.pg.index / S.pg.uniqueIndex (column names or expressions, where, using) and S.pg.foreignKey.
  • Primary keys can be composite.
  • Columns are NOT NULL unless PG.nullable.
  • Types are stored in format_type spelling.
• Diff: columns change in place (type, nullability, default, identity). Primary keys, indexes and foreign keys are dropped and re-created. Drops still need confirmation, and type changes are labelled rewrite.
• Runtime: each migration runs in one transaction together with its ledger row, under pg_advisory_xact_lock. MigrationDriver gains an optional transaction, which fromSqlClient provides.
• Drift: verify renders the snapshot into a scratch schema inside a transaction that is always rolled back, then reads both catalogs with the same queries. Postgres deparses both sides, so there's no heuristic SQL normalization.

Adopting drizzle-kit

• drizzle-kit snapshot.json files are recognized and kept aside.
• Migrations before the first effect-orm snapshot are treated as legacy.
• generate --baseline [--from-drizzle] starts the history, either from the definitions or from drizzle-kit's last snapshot.
• effect-orm baseline <name> / Migrate.baseline records already-applied migrations without running them.

Reviewer notes

• Breaking type changes:
  • Snapshot is now a union (ClickHouseSnapshot | PgSnapshot), and so is MigrationFile (ClickHouseMigrationFile | PgMigrationFile).
  • DiffResult is generic over its op type.
  • Drift.problem adds not_null, identity and foreign_key.
• Behaviour change in check: migrations without a snapshot are now accepted when they sort before the first one that has a snapshot. Previously every migration without a snapshot was an error.
• Not modelled yet: check and unique constraints, enums, views, non-public schemas, CREATE INDEX CONCURRENTLY, rename detection.
• Design notes are in design/migrations.md §8; user docs are in docs/migrations.md#postgres.

Testing

• bun run test: 606 passing, plus the citation, export-catalog and doc-example checks. 30 of the tests are new, including end-to-end PGlite runs: apply, rerun, rollback on failure, strict hash check, every kind of drift, and baseline adoption.
• Live ClickHouse: the suites (tests/, 281 tests, migrations included) pass against a fresh clickhouse-server:26.2.
• Maple's real migration folder: all 76 drizzle-kit migrations (373 statements) applied through the Postgres runner on PGlite. I then baselined --from-drizzle and ran verify. The only drift it reported is two objects Maple's SQL created and never dropped: the ai_triage_runs table and the ai_triage_settings.fanout_enabled column. Both are real orphans that drizzle-kit's snapshot misses.

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Summary by CodeRabbit

• New Features
  • Added PostgreSQL schema definitions and migration support, including migration generation, transactional execution, status tracking, and schema drift checks.
  • Added baseline workflows for existing databases and Drizzle Kit migration folders, so previously applied migrations can be recorded without rerunning them.
  • Added PostgreSQL schema import from Drizzle Kit snapshots, with diagnostics for unsupported objects.
• Documentation
  • Expanded migration guides to cover PostgreSQL, baselines, and Drizzle Kit adoption.

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📝 Walkthrough

Walkthrough

This change adds PostgreSQL schema definitions, migration generation and execution, catalog-based drift verification, and drizzle-kit baseline adoption. ClickHouse remains supported through its existing migration paths.

Changes

PostgreSQL support

Layer / File(s)	Summary
Schema model and definitions src/schema/entities.ts, src/schema/pg-entities.ts, src/schema/pg-define.ts, src/schema/snapshot.ts, src/schema.ts, src/schema/pg-schema.test.ts, docs/migrations.md	Adds PostgreSQL schema entities and table definitions, dialect-specific snapshots, schema validation, and public exports.
Schema diffs and SQL rendering src/schema/pg-diff.ts, src/schema/pg-ops.ts, src/schema/diff.ts, src/schema/ops.ts, src/schema/pg-schema.test.ts, docs/migrations.md	Adds PostgreSQL diff operations, migration-file definitions, and SQL rendering. Drops of tables and columns require matching data-loss hints.
Generation and drizzle-kit adoption src/kit/generate.ts, src/kit/graph.ts, src/kit/cli.ts, src/migrate/source.ts, src/schema/drizzle.ts, src/kit/kit.test.ts, src/schema/pg-schema.test.ts, docs/migrations.md, docs/README.md, design/gap-review.md	Adds dialect selection, drizzle-kit snapshot conversion, legacy migration handling, and schema- or Drizzle-based baseline generation.
Migration execution and verification src/migrate/driver.ts, src/migrate/pg-ledger.ts, src/migrate/run.ts, src/migrate/pg-verify.ts, src/migrate/verify.ts, src/kit/cli.ts, src/migrate/pg-migrate.test.ts, docs/migrations.md, design/migrations.md, CHANGELOG.md	Adds transactional PostgreSQL migration execution and ledger recording, baseline recording, dialect-aware status, and catalog-based drift verification.

Estimated code review effort: 4 (Complex) | ~60 minutes

Change: Feature

Sequence Diagram(s)

sequenceDiagram
  participant KitCLI
  participant MigrateRun
  participant MigrationDriver
  participant PostgreSQL
  KitCLI->>MigrateRun: Run migrations with configured dialect
  MigrateRun->>MigrationDriver: Start migration transaction
  MigrationDriver->>PostgreSQL: Acquire transaction-scoped advisory lock
  MigrateRun->>PostgreSQL: Execute migration statements
  MigrateRun->>PostgreSQL: Record migration name and hash
  MigrationDriver->>PostgreSQL: Commit transaction

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🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 23 files. (5 skipped: …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the primary change: adding PostgreSQL schema definitions and migrations.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 23 files. (5 skipped: 5 unsupported.)

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Actionable comments posted: 1

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• 🪄 Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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Inline comments:
Review comments at @src/schema/pg-define.ts:
- Around line 312-313: Update the default foreign-key name generation near
fkName so generated names stay within PostgreSQL’s 63-byte identifier limit,
matching drizzle-kit’s truncation or hashing behavior and keeping converted
baseline names stable; preserve explicitly supplied spec.name values and the
existing identifier validation.

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ℹ️ Review info

⚙️ Run configuration

• Configuration used: defaults
• Review profile: CHILL
• Plan: Advanced
• Run ID: 74f6c5f0-2c67-4c52-8730-443dfff980ee

📥 Commits

Reviewing files that changed from the base of the PR and between be1a3ec and 0aa9f8f.

📒 Files selected for processing (28)

• CHANGELOG.md
• design/gap-review.md
• design/migrations.md
• docs/README.md
• docs/migrations.md
• src/kit/cli.ts
• src/kit/generate.ts
• src/kit/graph.ts
• src/kit/kit.test.ts
• src/migrate.ts
• src/migrate/driver.ts
• src/migrate/pg-ledger.ts
• src/migrate/pg-migrate.test.ts
• src/migrate/pg-verify.ts
• src/migrate/run.ts
• src/migrate/source.ts
• src/migrate/verify.ts
• src/schema.ts
• src/schema/diff.ts
• src/schema/drizzle.ts
• src/schema/entities.ts
• src/schema/ops.ts
• src/schema/pg-define.ts
• src/schema/pg-diff.ts
• src/schema/pg-entities.ts
• src/schema/pg-ops.ts
• src/schema/pg-schema.test.ts
• src/schema/snapshot.ts

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