feat(db): atomic update expressions — d.expr, d.increment, d.decrement (#1743)

[viniciusdacal]

Summary

Adds atomic column-level update expressions to @vertz/db, enabling database-side operations without read-modify-write cycles.

• d.increment(n) / d.decrement(n) — atomic arithmetic on numeric columns
• **d.expr(col => sql\...`)** — arbitrary SQL expressions (e.g. LOWER(), COALESCE()`)
• Works in update, updateMany, upsert, and ON CONFLICT DO UPDATE SET
• Full PostgreSQL and SQLite dialect support
• Type-safe: $update and $update_input accept InferColumnType<T> | DbExpr

Public API Changes

New exports from @vertz/db

• DbExpr (type) — expression descriptor interface
• isDbExpr() — type guard
• sql — re-exported tagged template for use with d.expr()
• SqlFragment (type) — for advanced expression composition

New methods on d

• d.expr(col => sql\...`)` — general-purpose column expression
• d.increment(n) — sugar for d.expr(col => sql\${col} + ${n}`)`
• d.decrement(n) — sugar for d.expr(col => sql\${col} - ${n}`)`

Bug fix

• autoUpdate() columns with user-provided DbExpr were silently overwritten by the NOW() sentinel because autoUpdate() sets isReadOnly: true, causing the readOnly filter to strip the expression before the autoUpdate guard could see it. Fixed by allowing DbExpr values through the readOnly filter on autoUpdate columns.

Files changed

• packages/db/src/sql/expr.ts — new DbExpr type and isDbExpr guard
• packages/db/src/d.ts — d.expr(), d.increment(), d.decrement()
• packages/db/src/sql/update.ts — DbExpr detection in SET clause
• packages/db/src/sql/insert.ts — DbExpr in ON CONFLICT DO UPDATE SET
• packages/db/src/sql/tagged.ts — exported renumberParamsWithDialect()
• packages/db/src/query/crud.ts — autoUpdate guard + readOnly bypass for DbExpr
• packages/db/src/schema/table.ts — widened $update / $update_input types
• packages/db/src/index.ts — re-exports
• packages/mint-docs/guides/db/queries.mdx — documentation

Test plan

• 13 unit tests for DbExpr, isDbExpr, d.expr(), d.increment(), d.decrement()
• 7 tests for DbExpr in buildUpdate (increment, decrement, expr, multi-param, mixed, now-override, constant)
• 3 tests for DbExpr in buildInsert ON CONFLICT (increment, expr, mixed)
• 3 SQLite dialect tests for DbExpr in buildUpdate and buildInsert
• 6 unit tests for renumberParamsWithDialect()
• 1 CRUD-level regression test for autoUpdate + DbExpr interaction
• Type-level tests (.test-d.ts) — positive and negative tests for DbExpr in $update and $update_input
• Typecheck clean (no new errors in changed files)
• turbo run build typecheck test --filter='@vertz/db' passes

Closes #1743

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