Keep what was typed when a target or webhook edit is refused (closes #381)

A refused save on the target edit page answered with a bare text page, losing the form and everything typed, and the webhook edit page came back with the stored values instead of the submitted ones. A refused target edit now shows the edit form again with the reason above it and every value submitted, with the same status codes as before; a refused webhook edit keeps the submitted name, description and retention. Target edits use the same validation as new targets, with no second copy; an encoding or database failure stays a logged 500. The browser test covers a refused save on both pages, and its main function is now a plain list of checks.

Model: opus-5-5

internal/handlers/source_management_test.go

@@ -509,6 +509,51 @@ func TestHandleSourceEditSubmit_InvalidRetentionIsRejected(
 	)
 }
 
+// TestHandleSourceEditSubmit_RefusedFormComesBack refuses an edit for
+// each reason the form can give and checks that the form comes back
+// with the reason and the name, description and retention submitted,
+// that the page still reports the stored retention, and that nothing
+// is saved.
+func TestHandleSourceEditSubmit_RefusedFormComesBack(t *testing.T) {
+	t.Parallel()
+
+	env := setupSourceTest(t)
+
+	refused := func(name, retention, reason string) {
+		t.Helper()
+
+		wh := seedWebhookWithRetention(t, env.db, 30)
+
+		submitted := wh
+		submitted.Name = name
+		submitted.Description = "a description worth keeping"
+
+		w := submitEdit(t, env, submitted, retention)
+		assert.Equal(t, http.StatusBadRequest, w.Code)
+
+		page := w.Body.String()
+		assert.Contains(t, page, `class="alert-error">`+reason)
+		assert.Contains(t, page, `name="name" value="`+name+`"`)
+		assert.Contains(t, page, ">a description worth keeping</textarea>")
+		assert.Contains(
+			t, page, `name="retention_days" value="`+retention+`"`,
+		)
+		assert.Contains(t, page, "Currently 30 days.")
+
+		var stored database.Webhook
+
+		require.NoError(
+			t, env.db.DB().First(&stored, "id = ?", wh.ID).Error,
+		)
+		assert.Equal(t, wh.Name, stored.Name)
+		assert.Empty(t, stored.Description)
+		assert.Equal(t, 30, stored.RetentionDays)
+	}
+
+	refused("", "45", "Name is required")
+	refused("kept-name", "nonsense", "Retention must be")
+}
+
 func TestHandleSourceEditSubmit_EmptyRetentionLeavesValueUnchanged(
 	t *testing.T,
 ) {
@@ -809,6 +854,10 @@ func TestHandleSourceEditSubmit_ArchiveNameTaken(t *testing.T) {
 	w := submitEdit(t, env, wh, "")
 	require.Equal(t, http.StatusConflict, w.Code)
 	assert.Contains(t, w.Body.String(), "archive-taken.db")
+	assert.Contains(
+		t, w.Body.String(), `name="name" value="`+renamedWebhookName+`"`,
+		"the form comes back with the name submitted",
+	)
 
 	var stored database.Webhook