feat(pgsql): unique constraints on apply, matching unique index names, FK deferral

- migration writer now emits unique constraints (direct apply and live diff
  previously dropped them); idempotent via the existing DO block
- unique constraint adopts a same-named model unique index with
  ADD CONSTRAINT ... UNIQUE USING INDEX instead of building a second index
- dbml reader names unnamed unique indexes ukey_<table>_<cols> to match the
  unique constraint naming
- foreign key deferral: Constraint.Deferrable/InitiallyDeferred are *bool
  (nil = unspecified, never diffed); writers emit DEFERRABLE, DEFERRABLE
  INITIALLY DEFERRED and NOT DEFERRABLE; live reader reads condeferrable and
  condeferred; dbml reader/writer support deferrable and initially deferred
- tests and README/naming docs updated

pkg/readers/dbml/README.md

@@ -86,16 +86,40 @@ Ref: posts.user_id > users.id [delete: cascade]
 - Table definitions with columns
 - Primary keys (`pk`)
 - Not null constraints (`not null`)
-- Unique constraints (`unique`)
+- Unique constraints (`unique`) → constraint `ukey_<table>_<col>`
 - Default values (`default`)
 - Inline references (`ref`)
 - Standalone `Ref` blocks
+- FK deferral: `deferrable`, `initially deferred` (see below)
 - Commented cross-file refs (`// Ref:` — see below)
 - Indexes and composite indexes
 - Table notes and column notes
 - Enums
 - Dialect directives (`@postgres:` / `@sqlite:` — see below)
 
+## Naming
+
+| Source | Generated name |
+| ------ | -------------- |
+| Column `[unique]` | constraint `ukey_<table>_<col>` |
+| Unnamed unique index | index `ukey_<table>_<cols>` (same name as the constraint on the same columns) |
+| Unnamed index | `idx_<table>_<cols>` |
+
+Explicit `name:` is never changed. Leading `_` in the table name is stripped.
+
+## FK deferral
+
+```
+col int [ref: > t.id, deferrable, initially deferred]
+Ref: a.x > b.id [delete: cascade, deferrable]
+```
+
+| Setting | SQL |
+| ------- | --- |
+| `deferrable` | `DEFERRABLE` |
+| `initially deferred` | `DEFERRABLE INITIALLY DEFERRED` |
+| neither | unspecified (existing FK left as is) |
+
 ## Commented cross-file refs
 
 `// Ref:` / `// ref:` lines (ignored by dbdiagram) become FKs + relationships once both ends are loaded.

pkg/readers/dbml/reader.go

@@ -848,6 +848,13 @@ func (r *Reader) parseColumn(line, tableName, schemaName string) (*models.Column
 		}
 	}
 
+	// "deferrable" / "initially deferred" column settings apply to the inline foreign key
+	if constraint != nil && constraint.Type == models.ForeignKeyConstraint && attrs != "" {
+		for _, attr := range splitColumnAttrs(attrs) {
+			applyDeferralSetting(constraint, attr)
+		}
+	}
+
 	// Parse inline comment
 	if inlineComment != "" {
 		column.Comment = inlineComment
@@ -1081,11 +1088,13 @@ func (r *Reader) parseIndex(line, tableName, schemaName string) *models.Index {
 
 	// Generate name if not provided
 	if index.Name == "" {
-		prefix := "idx"
+		// Unique indexes share the ukey_ naming of unique constraints, so an index and a
+		// constraint on the same columns get the same name and can be merged on write.
+		prefix, name := "idx", tableName
 		if index.Unique {
-			prefix = "uidx"
+			prefix, name = "ukey", strings.TrimLeft(tableName, "_")
 		}
-		index.Name = fmt.Sprintf("%s_%s_%s", prefix, tableName, strings.Join(columns, "_"))
+		index.Name = fmt.Sprintf("%s_%s_%s", prefix, name, strings.Join(columns, "_"))
 	}
 
 	return index
@@ -1182,6 +1191,8 @@ func (r *Reader) parseRef(refStr string) *models.Constraint {
 					constraint.OnDelete = strings.TrimSpace(strings.TrimPrefix(action, "ondelete:"))
 				} else if strings.HasPrefix(action, "onupdate:") {
 					constraint.OnUpdate = strings.TrimSpace(strings.TrimPrefix(action, "onupdate:"))
+				} else {
+					applyDeferralSetting(constraint, action)
 				}
 			}
 		}
@@ -1190,6 +1201,18 @@ func (r *Reader) parseRef(refStr string) *models.Constraint {
 	return constraint
 }
 
+// applyDeferralSetting applies a "deferrable" or "initially deferred" Ref setting to a
+// foreign key constraint. Other settings are ignored.
+func applyDeferralSetting(constraint *models.Constraint, setting string) {
+	yes := true
+	switch strings.Join(strings.Fields(strings.ToLower(setting)), " ") {
+	case "deferrable":
+		constraint.Deferrable = &yes
+	case "initially deferred", "initially_deferred":
+		constraint.InitiallyDeferred = &yes
+	}
+}
+
 // parseTableRef parses a table reference like "schema.table.(column1, column2)" or "schema"."table"."column"
 func (r *Reader) parseTableRef(ref string) (schema, table string, columns []string) {
 	// Extract columns if present in parentheses format

pkg/readers/dbml/reader_test.go

@@ -3,6 +3,7 @@ package dbml
 import (
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 
 	"git.warky.dev/wdevs/relspecgo/pkg/models"
@@ -842,9 +843,9 @@ func TestConstraintNaming(t *testing.T) {
 		t.Logf("Available constraints: %v", getKeys(postsTable.Constraints))
 	}
 
-	// Test unique index naming: uidx_table_columns
-	if _, exists := postsTable.Indexes["uidx_posts_slug"]; !exists {
-		t.Error("Expected unique index 'uidx_posts_slug' not found")
+	// Test unique index naming: ukey_table_columns, matching the unique constraint name
+	if _, exists := postsTable.Indexes["ukey_posts_slug"]; !exists {
+		t.Error("Expected unique index 'ukey_posts_slug' not found")
 		t.Logf("Available indexes: %v", getKeys(postsTable.Indexes))
 	}
 
@@ -1121,3 +1122,69 @@ func TestReader_DuplicateIndexNameInTableKept(t *testing.T) {
 		}
 	}
 }
+
+func TestReader_ForeignKeyDeferral(t *testing.T) {
+	dbml := `Table users {
+  id integer [pk]
+}
+
+Table posts {
+  id integer [pk]
+  user_id integer [ref: > users.id, deferrable, initially deferred]
+  editor_id integer
+  plain_id integer [ref: > users.id]
+}
+
+Table comments {
+  id integer [pk]
+  post_id integer
+  author_id integer
+}
+
+Ref: comments.post_id > posts.id [delete: cascade, deferrable]
+Ref: comments.author_id > users.id [deferrable, initially deferred]
+`
+	path := filepath.Join(t.TempDir(), "deferral.dbml")
+	if err := os.WriteFile(path, []byte(dbml), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	db, err := NewReader(&readers.ReaderOptions{FilePath: path}).ReadDatabase()
+	if err != nil {
+		t.Fatalf("ReadDatabase() error = %v", err)
+	}
+
+	find := func(table, column string) *models.Constraint {
+		for _, s := range db.Schemas {
+			for _, tb := range s.Tables {
+				if tb.Name != table {
+					continue
+				}
+				for _, c := range tb.Constraints {
+					if c.Type == models.ForeignKeyConstraint && len(c.Columns) == 1 && c.Columns[0] == column {
+						return c
+					}
+				}
+			}
+		}
+		t.Fatalf("FK %s.%s not found", table, column)
+		return nil
+	}
+
+	tests := []struct {
+		table, column string
+		want          string
+	}{
+		{"posts", "user_id", "DEFERRABLE INITIALLY DEFERRED"},
+		{"posts", "plain_id", ""},
+		{"comments", "post_id", "DEFERRABLE"},
+		{"comments", "author_id", "DEFERRABLE INITIALLY DEFERRED"},
+	}
+	for _, tt := range tests {
+		if got := find(tt.table, tt.column).DeferralClause(); got != tt.want {
+			t.Errorf("%s.%s deferral = %q, want %q", tt.table, tt.column, got, tt.want)
+		}
+	}
+	if got := find("comments", "post_id").OnDelete; !strings.EqualFold(got, "cascade") {
+		t.Errorf("delete action lost, got %q", got)
+	}
+}