Allow retention_days of 0 to mean retain forever (closes #79)

RetentionDays carried gorm:"default:30", so GORM substituted 30 for a
zero value while building the insert. A webhook could therefore never
be configured to keep its events indefinitely: the reaper's
retain-forever branch existed but was unreachable from the normal
create and edit flows.

Introduce database.RetentionForeverDays = 365 * 1000 as the sentinel
for "retain forever" and a Webhook.BeforeSave hook that rewrites any
non-positive RetentionDays to it. The rewrite has to live in the hook
rather than at the call sites: GORM applies the column default while
converting the model to insert values, which happens after BeforeSave,
so anything later loses that race. Putting it on the model also means
a future call site, such as the planned REST API, cannot bypass it.

The reaper now skips a webhook when Webhook.RetainsForever reports
true, which recognises the sentinel and keeps honouring the old <= 0
values for rows written before it existed. Without this the sentinel,
being positive, would have produced a cutoff a thousand years in the
past and a DELETE matching nothing on every sweep.

Form handling is shared by create and edit through parseRetentionDays
so the two cannot drift: an empty field keeps the previous behaviour
(default on create, unchanged on edit), 0 is honoured, and an
unparseable or negative value is a 400 that re-renders the form rather
than a silently substituted default.

The retention inputs drop max="365". That cap was not cosmetic: the
edit form pre-fills the stored value, so a retain-forever webhook
rendered 365000 into an input capped at 365 and browser validation
would have blocked saving any edit to it. min becomes 0 with a hint
explaining what 0 does, and the list and detail views render a
RetentionLabel of "forever" instead of a raw day count.

The 30-day default is consolidated into database.DefaultRetentionDays,
referenced from the handler and from the create form's pre-filled
value, with a test asserting it agrees with the struct tag that cannot
reference it.

internal/database/model_webhook_test.go

@@ -0,0 +1,184 @@
+package database_test
+
+import (
+	"context"
+	"reflect"
+	"strconv"
+	"testing"
+
+	"github.com/google/uuid"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"gorm.io/gorm"
+	"gorm.io/gorm/clause"
+	"sneak.berlin/go/webhooker/internal/database"
+)
+
+// startedTestDB returns a started main database for model-level tests.
+func startedTestDB(t *testing.T) *gorm.DB {
+	t.Helper()
+
+	db, lc := setupTestDB(t)
+
+	ctx := context.Background()
+	require.NoError(t, lc.Start(ctx))
+	t.Cleanup(func() { require.NoError(t, lc.Stop(ctx)) })
+
+	return db.DB()
+}
+
+// storedRetention reads the retention_days column straight out of the
+// row, so the assertion is about what was persisted rather than about
+// whatever the in-memory struct happens to hold.
+func storedRetention(t *testing.T, db *gorm.DB, id string) int {
+	t.Helper()
+
+	var got int
+
+	require.NoError(
+		t,
+		db.Model(&database.Webhook{}).
+			Where("id = ?", id).
+			Pluck("retention_days", &got).Error,
+	)
+
+	return got
+}
+
+// newWebhookWithRetention creates a webhook through the ordinary Create
+// path, so the BeforeSave hook and the GORM column default both apply
+// exactly as they do in production.
+func newWebhookWithRetention(
+	t *testing.T,
+	db *gorm.DB,
+	wh *database.Webhook,
+) string {
+	t.Helper()
+
+	wh.UserID = uuid.New().String()
+	wh.Name = testWebhookName
+
+	require.NoError(
+		t,
+		db.Omit(clause.Associations).Create(wh).Error,
+	)
+
+	return wh.ID
+}
+
+func TestWebhookBeforeSave_ZeroBecomesForeverSentinel(t *testing.T) {
+	t.Parallel()
+
+	db := startedTestDB(t)
+
+	wh := &database.Webhook{RetentionDays: 0}
+	id := newWebhookWithRetention(t, db, wh)
+
+	assert.Equal(
+		t,
+		database.RetentionForeverDays,
+		storedRetention(t, db, id),
+		"a zero retention must be stored as the sentinel, "+
+			"not replaced by the column default",
+	)
+}
+
+func TestWebhookBeforeSave_NegativeBecomesForeverSentinel(t *testing.T) {
+	t.Parallel()
+
+	db := startedTestDB(t)
+
+	wh := &database.Webhook{RetentionDays: -5}
+	id := newWebhookWithRetention(t, db, wh)
+
+	assert.Equal(
+		t,
+		database.RetentionForeverDays,
+		storedRetention(t, db, id),
+	)
+}
+
+func TestWebhookBeforeSave_PositiveIsPreserved(t *testing.T) {
+	t.Parallel()
+
+	db := startedTestDB(t)
+
+	wh := &database.Webhook{RetentionDays: 7}
+	id := newWebhookWithRetention(t, db, wh)
+
+	assert.Equal(t, 7, storedRetention(t, db, id))
+}
+
+// TestWebhookBeforeSave_UpdateToZeroBecomesSentinel proves the hook
+// fires on update as well as insert, via the same Save call the edit
+// handler makes.
+func TestWebhookBeforeSave_UpdateToZeroBecomesSentinel(t *testing.T) {
+	t.Parallel()
+
+	db := startedTestDB(t)
+
+	wh := &database.Webhook{RetentionDays: 30}
+	id := newWebhookWithRetention(t, db, wh)
+	require.Equal(t, 30, storedRetention(t, db, id))
+
+	wh.RetentionDays = 0
+	require.NoError(t, db.Omit(clause.Associations).Save(wh).Error)
+
+	assert.Equal(
+		t,
+		database.RetentionForeverDays,
+		storedRetention(t, db, id),
+	)
+}
+
+// TestWebhookRetentionColumnDefaultMatchesConstant guards the one place
+// the default lives twice: a struct tag cannot reference a constant, so
+// this asserts the tag and DefaultRetentionDays agree.
+func TestWebhookRetentionColumnDefaultMatchesConstant(t *testing.T) {
+	t.Parallel()
+
+	field, ok := reflect.TypeFor[database.Webhook]().
+		FieldByName("RetentionDays")
+	require.True(t, ok, "Webhook.RetentionDays must exist")
+
+	assert.Equal(
+		t,
+		"default:"+strconv.Itoa(database.DefaultRetentionDays),
+		field.Tag.Get("gorm"),
+	)
+}
+
+func TestWebhookRetainsForeverAndLabel(t *testing.T) {
+	t.Parallel()
+
+	cases := []struct {
+		name    string
+		days    int
+		forever bool
+		label   string
+	}{
+		{
+			"sentinel",
+			database.RetentionForeverDays, true, testForeverLabel,
+		},
+		{
+			"above sentinel",
+			database.RetentionForeverDays + 1, true, testForeverLabel,
+		},
+		{"legacy zero", 0, true, testForeverLabel},
+		{"legacy negative", -1, true, testForeverLabel},
+		{"default", database.DefaultRetentionDays, false, "30 days"},
+		{"one day", 1, false, "1 day"},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			wh := database.Webhook{RetentionDays: tc.days}
+
+			assert.Equal(t, tc.forever, wh.RetainsForever())
+			assert.Equal(t, tc.label, wh.RetentionLabel())
+		})
+	}
+}