fix(10.1): CR-01 answer a value that does not fit its column with a 422

lagoon.Fill now returns a *lagoon.FillTypeError naming the key when a
requested value cannot be stored in its column (a fraction, exponent or
overflow for an integer field, or a value of the wrong type). The admin
save path maps it to a validation_failed 422 on that field instead of a
500 CapabilityError; genuine capability failures keep the 500.

modules/lagoon/README.md

@@ -15,7 +15,7 @@ Postgres data layer: the shared GORM connection, per-plugin migrations, model he
 - One shared pool: `lagoon.Open`, `lagoon.Use` and `lagoon.OpenFromApp` return a `*sql.DB` and a `*gorm.DB` built on that same pool; `lagoon.Publish` makes both available on the `backpack.App`.
 - Database check at connect time: `lagoon.CheckLocale` refuses a database whose default collation is not the ICU `pl-PL` locale, so ordering matches the database default without per-query `COLLATE`.
 - Per-plugin migrations: `lagoon.Migrate` runs the framework's `system_files` set (`attach.Migrations`) and backend admin identity set (`lagoon.BackendAdminMigrations`), then every `pact.HasMigrations` set in plugin activation order, each in its own `summer_migrations_<plugin_id>` history table (`lagoon.HistoryTableName`). `lagoon.RollbackLast` and `lagoon.Status` cover rollback and history.
-- Mass assignment: `lagoon.Fill` copies only allow-listed keys onto a model by GORM column name and silently drops the rest, logging each dropped key once outside production. A `json.Number` (from a decoder using `UseNumber`) fills integer, unsigned and float fields, and a fraction or an overflow is an error. `lagoon.HasFillable` and `lagoon.HasHidden` are the Go forms of `$fillable` and `$hidden`.
+- Mass assignment: `lagoon.Fill` copies only allow-listed keys onto a model by GORM column name and silently drops the rest, logging each dropped key once outside production. A `json.Number` (from a decoder using `UseNumber`) fills integer, unsigned and float fields. A value that does not fit its column (a fraction, an exponent or an overflow for an integer field, or a value of the wrong type) is a `lagoon.FillTypeError` naming the key, so a caller can answer it as a validation failure on that field. `lagoon.HasFillable` and `lagoon.HasHidden` are the Go forms of `$fillable` and `$hidden`.
 - Validation: `lagoon.Validate` accepts Laravel-style rule strings (`required`, `nullable`, `integer`, `numeric`, `between`, `min`, `max`, `in`, `unique`, `boolean`, `email`, `confirmed`, `different`, `mimes`) and returns a field-to-messages map, translated through phrasebook when a translator is given. Unknown rule tokens are an error.
 - Safe ordering: `lagoon.OrderBy` appends an ORDER BY only for an allow-listed column and an `asc` or `desc` direction.
 - Pagination: `lagoon.Paginate` builds a `lagoon.Page` with `data` and `meta` (`current_page`, `last_page`, `per_page`, `total`).
@@ -102,6 +102,7 @@ func (p *Plugin) Migrations() []*gormigrate.Migration {
 | `lagoon.Encrypted` | Encrypted text column; `lagoon.Encrypted.Reveal` is the only plaintext accessor. |
 | `lagoon.Jsonable` | Generic JSON-as-TEXT column with NULL tracking. |
 | `lagoon.Fill` | Allow-listed mass assignment by column name. |
+| `lagoon.FillTypeError` | Returned by `lagoon.Fill` when a requested value does not fit its column; `Key` names the column. |
 | `lagoon.Validate` | Laravel-style rule validation with a `unique` database check. |
 | `lagoon.OrderBy` | Allow-listed ORDER BY. |
 | `lagoon.Paginate` | Builds a `lagoon.Page` with `lagoon.PageMeta`. |

modules/lagoon/fill.go

@@ -25,9 +25,25 @@ type HasHidden interface {
 
 var droppedKeys sync.Map
 
+// FillTypeError reports a requested value that cannot be stored in its
+// column: a fraction, an exponent or an overflow for an integer field, or a
+// value of the wrong type. Key is the column the value was requested for, so
+// a caller can answer it as a validation failure on that field. Fill returns
+// any other failure, such as a model that is not a struct pointer, as a
+// plain error.
+type FillTypeError struct {
+	Key string
+	Err error
+}
+
+func (e *FillTypeError) Error() string { return "lagoon: fill " + e.Key + ": " + e.Err.Error() }
+
+func (e *FillTypeError) Unwrap() error { return e.Err }
+
 // Fill copies requested keys onto model only when they are also in allowed.
 // Unknown and non-fillable keys are dropped with no error (D-06). In
-// non-production, each type+key pair is logged once.
+// non-production, each type+key pair is logged once. A value that does not
+// fit its column is a *FillTypeError.
 func Fill(model any, allowed []string, requested map[string]any, production bool) error {
 	if model == nil {
 		return fmt.Errorf("lagoon: fill model is nil")
@@ -53,7 +69,7 @@ func Fill(model any, allowed []string, requested map[string]any, production bool
 			continue
 		}
 		if err := setField(field, val); err != nil {
-			return fmt.Errorf("lagoon: fill %s: %w", key, err)
+			return &FillTypeError{Key: key, Err: err}
 		}
 	}
 	return nil

modules/lagoon/fill_test.go

@@ -3,6 +3,7 @@ package lagoon
 import (
 	"bytes"
 	"encoding/json"
+	"errors"
 	"log/slog"
 	"strings"
 	"testing"
@@ -193,3 +194,38 @@ func TestFillJSONNumber(t *testing.T) {
 		}
 	}
 }
+
+// TestFillTypeErrorNamesTheKey proves a value that does not fit its column
+// comes back as a *FillTypeError carrying the requested key, so a caller can
+// answer it as a validation failure on that field, while a bad model stays a
+// plain error.
+func TestFillTypeErrorNamesTheKey(t *testing.T) {
+	type numbers struct {
+		Year  int     `gorm:"column:year"`
+		Count uint8   `gorm:"column:count"`
+		Title string  `gorm:"column:title"`
+		Price float64 `gorm:"column:price"`
+	}
+	allowed := []string{"year", "count", "title", "price"}
+	cases := map[string]any{
+		"year":  json.Number("1977.5"),
+		"count": json.Number("1e21"),
+		"title": true,
+		"price": "cheap",
+	}
+	for key, value := range cases {
+		var row numbers
+		err := Fill(&row, allowed, map[string]any{key: value}, true)
+		var typed *FillTypeError
+		if !errors.As(err, &typed) || typed.Key != key || typed.Err == nil {
+			t.Fatalf("%s = %v: err = %#v, want *FillTypeError for %s", key, value, err, key)
+		}
+		if !strings.Contains(err.Error(), "lagoon: fill "+key+": ") {
+			t.Fatalf("%s: message = %q", key, err.Error())
+		}
+	}
+	var typed *FillTypeError
+	if err := Fill(numbers{}, allowed, map[string]any{"year": 1}, true); err == nil || errors.As(err, &typed) {
+		t.Fatalf("non-pointer model: err = %v, want a plain error", err)
+	}
+}