diff --git a/e2e/trino/connection-form.spec.ts b/e2e/trino/connection-form.spec.ts
index 0467eff3..ab7aa778 100644
--- a/e2e/trino/connection-form.spec.ts
+++ b/e2e/trino/connection-form.spec.ts
@@ -32,7 +32,12 @@ function interceptSaveSuccess(page: import('@playwright/test').Page) {
         valid: true,
         posted: true,
         errors: {},
-        data: { connectionUrl: 'http://localhost:8080', authType: 'none' },
+        data: {
+          connectionUrl: 'http://localhost:8080',
+          authType: 'none',
+          authUsername: '',
+          authPassword: ''
+        },
         message: { type: 'success' }
       };
       await route.fulfill({
@@ -90,7 +95,7 @@ test.describe('Connection form (env-configured)', () => {
     await page.goto('/trino');
     await waitForHydration(page);
 
-    await expect(page.getByText('Connection', { exact: true })).not.toBeVisible();
+    await expect(page.getByText('Edit connection', { exact: true })).not.toBeVisible();
     await expect(page.locator('input[type="url"]')).not.toBeVisible();
   });
 });
@@ -117,25 +122,27 @@ test.describe('Connection form (manual mode)', () => {
     await page.goto('/trino');
     await waitForHydration(page);
 
-    await expect(page.getByText('Connection', { exact: true })).toBeVisible();
+    await expect(page.getByText('Edit connection', { exact: true })).toBeVisible();
   });
 
-  test('expanding the form reveals URL input', async ({ page }) => {
+  test('form is expanded initially when there is no connection', async ({ page }) => {
     await page.goto('/trino');
     await waitForHydration(page);
 
-    // Click the collapse toggle to open the form.
-    await page.getByLabel('Connection').check();
-
+    await expect(page.getByLabel('Edit connection')).toBeChecked();
     await expect(page.getByLabel('URL')).toBeVisible();
     await expect(page.getByRole('button', { name: 'Save' })).toBeVisible();
+
+    // The collapse toggle still hides the form.
+    await page.getByLabel('Edit connection').uncheck();
+    await expect(page.getByLabel('URL')).not.toBeVisible();
   });
 
   test('auth type toggle shows credential fields for basic auth', async ({ page }) => {
     await page.goto('/trino');
     await waitForHydration(page);
 
-    await page.getByLabel('Connection').check();
+    await page.getByLabel('Edit connection').check();
 
     // Initially no credential fields (auth type defaults to "none").
     await expect(page.getByLabel('Username')).not.toBeVisible();
@@ -152,7 +159,7 @@ test.describe('Connection form (manual mode)', () => {
     await page.goto('/trino');
     await waitForHydration(page);
 
-    await page.getByLabel('Connection').check();
+    await page.getByLabel('Edit connection').check();
 
     // Switch to basic, then back to no auth.
     await page.getByRole('radio', { name: 'Basic' }).click();
@@ -167,7 +174,7 @@ test.describe('Connection form (manual mode)', () => {
     await page.goto('/trino');
     await waitForHydration(page);
 
-    await page.getByLabel('Connection').check();
+    await page.getByLabel('Edit connection').check();
 
     // Submit with empty URL.
     await page.getByRole('button', { name: 'Save' }).click();
@@ -176,11 +183,25 @@ test.describe('Connection form (manual mode)', () => {
     await expect(page.locator('.text-error')).toBeVisible();
   });
 
+  test('invalid URL shows a translated validation message', async ({ page }) => {
+    await page.goto('/trino');
+    await waitForHydration(page);
+
+    await page.getByLabel('Edit connection').check();
+
+    await page.getByLabel('URL').fill('not a url');
+    await page.getByRole('button', { name: 'Save' }).click();
+
+    await expect(
+      page.getByText('Enter a valid URL, e.g. https://trino.example.com:8443.')
+    ).toBeVisible();
+  });
+
   test('basic auth requires username and password', async ({ page }) => {
     await page.goto('/trino');
     await waitForHydration(page);
 
-    await page.getByLabel('Connection').check();
+    await page.getByLabel('Edit connection').check();
 
     // Fill URL but leave credentials empty with basic auth selected.
     await page.getByLabel('URL').fill('http://localhost:8080');
@@ -197,7 +218,7 @@ test.describe('Connection form (manual mode)', () => {
     await page.goto('/trino');
     await waitForHydration(page);
 
-    await page.getByLabel('Connection').check();
+    await page.getByLabel('Edit connection').check();
 
     const testUrl = 'http://localhost:8080';
     await page.getByLabel('URL').fill(testUrl);
@@ -217,7 +238,7 @@ test.describe('Connection form (manual mode)', () => {
     await page.goto('/trino');
     await waitForHydration(page);
 
-    await page.getByLabel('Connection').check();
+    await page.getByLabel('Edit connection').check();
 
     // The URL field should be pre-filled from localStorage.
     await expect(page.getByLabel('URL')).toHaveValue('http://localhost:8080');
@@ -236,6 +257,41 @@ test.describe('Connection form (manual mode)', () => {
     await expect(page.getByText('localhost:8080')).toBeVisible();
   });
 
+  test('failed reconnect of a stored connection opens the form with the error', async ({
+    page
+  }) => {
+    await page.addInitScript(() => {
+      localStorage.setItem('trino_url', 'http://localhost:8080');
+      localStorage.setItem('trino_auth_type', 'none');
+    });
+
+    // The server is env-configured, so the automatic reconnect is rejected.
+    await page.goto('/trino');
+    await waitForHydration(page);
+
+    await expect(
+      page.getByText('The connection is managed via environment variables.')
+    ).toBeVisible();
+    await expect(page.getByLabel('URL')).toHaveValue('http://localhost:8080');
+  });
+
+  test('network error during reconnect opens the form with the error', async ({ page }) => {
+    await page.addInitScript(() => {
+      localStorage.setItem('trino_url', 'http://localhost:8080');
+      localStorage.setItem('trino_auth_type', 'none');
+    });
+    await page.route(
+      (url) => url.pathname === '/trino' && url.search === '?/save',
+      (route) => route.abort()
+    );
+
+    await page.goto('/trino');
+    await waitForHydration(page);
+
+    await expect(page.getByText('Could not save the connection. Please try again.')).toBeVisible();
+    await expect(page.getByLabel('URL')).toHaveValue('http://localhost:8080');
+  });
+
   test('saving a connection clears previous query results', async ({ page }) => {
     await setTabSql(page, 'SELECT id, name FROM users');
     interceptSaveSuccess(page);
@@ -249,7 +305,7 @@ test.describe('Connection form (manual mode)', () => {
     await waitForQueryComplete(page);
     await expect(page.getByRole('table', { name: 'Query results' })).toBeVisible();
 
-    await page.getByLabel('Connection').check();
+    await page.getByLabel('Edit connection').check();
     await page.getByLabel('URL').fill('http://localhost:8080');
     await page.getByRole('button', { name: 'Save' }).click();
 
diff --git a/messages/de.json b/messages/de.json
index 6173dea8..8431a757 100644
--- a/messages/de.json
+++ b/messages/de.json
@@ -58,7 +58,7 @@
   "trino_prev_page": "Vorherige Seite",
   "trino_next_page": "Nächste Seite",
   "trino_last_page": "Letzte Seite",
-  "trino_connection_label": "Verbindung",
+  "trino_connection_label": "Verbindung bearbeiten",
   "trino_connection_error": "Bitte konfigurieren Sie eine gültige Verbindungs-URL.",
   "trino_connection_url": "URL",
   "trino_connection_auth": "Authentifizierung",
@@ -68,6 +68,13 @@
   "trino_auth_password": "Passwort",
   "trino_save_connection": "Speichern",
   "trino_connection_saved": "Verbindung gespeichert.",
+  "trino_connection_url_invalid": "Bitte eine gültige URL eingeben, z. B. https://trino.example.com:8443.",
+  "trino_auth_username_required": "Für Basic-Authentifizierung ist ein Benutzername erforderlich",
+  "trino_auth_password_required": "Für Basic-Authentifizierung ist ein Passwort erforderlich",
+  "trino_connection_test_timeout": "Zeitüberschreitung beim Verbindungstest",
+  "trino_connection_test_failed": "Verbindung zu Trino fehlgeschlagen – bitte URL und Zugangsdaten prüfen.",
+  "trino_connection_save_failed": "Die Verbindung konnte nicht gespeichert werden. Bitte erneut versuchen.",
+  "trino_connection_env_managed": "Die Verbindung wird über Umgebungsvariablen verwaltet.",
   "trino_cancel_query": "Abbrechen",
   "trino_state_submitting": "Wird eingereicht",
   "trino_state_queued": "Warteschlange",
diff --git a/messages/en.json b/messages/en.json
index b9216ce0..92a586a0 100644
--- a/messages/en.json
+++ b/messages/en.json
@@ -58,7 +58,7 @@
   "trino_prev_page": "Previous page",
   "trino_next_page": "Next page",
   "trino_last_page": "Last page",
-  "trino_connection_label": "Connection",
+  "trino_connection_label": "Edit connection",
   "trino_connection_error": "Please configure a valid connection URL.",
   "trino_connection_url": "URL",
   "trino_connection_auth": "Auth",
@@ -68,6 +68,13 @@
   "trino_auth_password": "Password",
   "trino_save_connection": "Save",
   "trino_connection_saved": "Connection saved.",
+  "trino_connection_url_invalid": "Enter a valid URL, e.g. https://trino.example.com:8443.",
+  "trino_auth_username_required": "Username is required for basic authentication",
+  "trino_auth_password_required": "Password is required for basic authentication",
+  "trino_connection_test_timeout": "Connection test timed out",
+  "trino_connection_test_failed": "Could not connect to Trino — check the URL and credentials.",
+  "trino_connection_save_failed": "Could not save the connection. Please try again.",
+  "trino_connection_env_managed": "The connection is managed via environment variables.",
   "trino_cancel_query": "Cancel",
   "trino_state_submitting": "Submitting",
   "trino_state_queued": "Queued",
diff --git a/src/routes/(app)/trino/+page.server.ts b/src/routes/(app)/trino/+page.server.ts
index 997eafe0..c6c00ad1 100644
--- a/src/routes/(app)/trino/+page.server.ts
+++ b/src/routes/(app)/trino/+page.server.ts
@@ -16,6 +16,7 @@ import {
 } from '$lib/server/trino/user-clients.js';
 import { ConnectionSchema, type ConnectionMessage } from './validation.js';
 import type { Actions, PageServerLoad } from './$types';
+import * as m from '$lib/paraglide/messages.js';
 
 export const load: PageServerLoad = async ({ locals }) => {
   locals.logger.debug('loading Trino page');
@@ -30,12 +31,17 @@ export const actions: Actions = {
   save: async ({ request, locals }) => {
     const log = locals.logger;
 
+    const form = await superValidate(request, zod(ConnectionSchema));
+
     if (trinoConfigured) {
-      return fail(400, { error: 'Connection is managed via environment variables' });
+      log.debug('connection save rejected, Trino is configured via environment variables');
+      return message(
+        form,
+        { type: 'error', message: m.trino_connection_env_managed() } satisfies ConnectionMessage,
+        { status: 400 }
+      );
     }
 
-    const form = await superValidate(request, zod(ConnectionSchema));
-
     if (!form.valid) {
       log.debug({ errors: form.errors }, 'connection form validation failed');
       return fail(400, { form });
@@ -64,8 +70,8 @@ export const actions: Actions = {
       const name = (err as { name?: string })?.name;
       const reason =
         name === 'TimeoutError' || name === 'AbortError'
-          ? 'Connection test timed out'
-          : 'Could not connect to Trino — check the URL and credentials.';
+          ? m.trino_connection_test_timeout()
+          : m.trino_connection_test_failed();
       log.info({ err, trino_url: connectionUrl }, 'connection test failed');
       return message(form, { type: 'error', message: reason } satisfies ConnectionMessage, {
         status: 400
diff --git a/src/routes/(app)/trino/+page.svelte b/src/routes/(app)/trino/+page.svelte
index e61e2d51..ae4e4434 100644
--- a/src/routes/(app)/trino/+page.svelte
+++ b/src/routes/(app)/trino/+page.svelte
@@ -1,5 +1,5 @@
 <script lang="ts">
-  import { onMount, untrack } from 'svelte';
+  import { onMount, tick, untrack } from 'svelte';
   import { SvelteMap } from 'svelte/reactivity';
   import { browser } from '$app/environment';
   import * as m from '$lib/paraglide/messages.js';
@@ -9,6 +9,7 @@
   import { createResizablePanel } from '$lib/components/storage/sidebar/resizable-panel.svelte.js';
   import Modal from '$lib/components/Modal.svelte';
   import { superForm } from 'sveltekit-superforms';
+  import { zod4Client } from 'sveltekit-superforms/adapters';
   import { ConnectionSchema, type ConnectionMessage } from './validation.js';
   import TabBar from '$lib/components/TabBar.svelte';
   import { tabStore, MAX_SQL_LENGTH } from '$lib/stores/tab-store.svelte.js';
@@ -39,12 +40,8 @@
     }
   }
 
-  // Connection config - local state persisted to localStorage.
-  let connectionUrl = $state('');
-  let authType = $state<'none' | 'basic'>('none');
-  let authUsername = $state('');
-  let authPassword = $state('');
-  let connectionOpen = $state(false);
+  // Start expanded until the user has a server-side connection, so the form is the first thing they see.
+  let connectionOpen = $state(untrack(() => !data.userClientExists));
 
   // Drag-to-resize state for the desktop catalog browser panel (width persisted).
   const catalogResize = createResizablePanel({
@@ -96,11 +93,46 @@
     }))
   );
 
+  // Connection form (SuperForms). Fields other than the password are persisted to localStorage.
+  const {
+    form: connectionForm,
+    enhance: connectionEnhance,
+    errors: connectionErrors,
+    message: connectionMessage,
+    submitting: connectionSubmitting,
+    submit: submitConnection
+  } = superForm(
+    untrack(() => data.connectionForm),
+    {
+      validators: zod4Client(ConnectionSchema),
+      // Keep the entered connection after a successful save instead of resetting to the defaults.
+      resetForm: false,
+      onUpdated({ form }) {
+        const msg = form.message as ConnectionMessage | undefined;
+        if (msg?.type === 'success') {
+          // Results belong to the previous connection; the server has cleared them too.
+          resetAllQueryRunners();
+          catalogVersion++;
+        } else if (msg?.type === 'error') {
+          connectionOpen = true;
+        }
+      },
+      // Network failures or unexpected server errors: show them in the form instead of the error page.
+      onError() {
+        $connectionMessage = {
+          type: 'error',
+          message: m.trino_connection_save_failed()
+        } satisfies ConnectionMessage;
+        connectionOpen = true;
+      }
+    }
+  );
+
   onMount(() => {
     if (!data.trinoConfigured) {
-      connectionUrl = getStoredValue('trino_url', '');
-      authType = getStoredValue('trino_auth_type', 'none') as 'none' | 'basic';
-      authUsername = getStoredValue('trino_username', '');
+      $connectionForm.connectionUrl = getStoredValue('trino_url', '');
+      $connectionForm.authType = getStoredValue('trino_auth_type', 'none') as 'none' | 'basic';
+      $connectionForm.authUsername = getStoredValue('trino_username', '');
     }
     defaultCatalog = getStoredValue('trino_default_catalog', '');
     defaultSchema = getStoredValue('trino_default_schema', '');
@@ -110,30 +142,14 @@
     if (data.trinoConfigured || data.userClientExists) {
       // Server already has a connection (env-based or per-user); load catalogues.
       catalogVersion++;
-    } else if (connectionUrl && authType === 'none') {
+    } else if ($connectionForm.connectionUrl && $connectionForm.authType === 'none') {
       // Re-establish server-side connection from localStorage on page reload.
       // Only possible for unauthenticated connections since the password is not persisted.
-      const body = new FormData();
-      body.set('connectionUrl', connectionUrl);
-      body.set('authType', authType);
-      body.set('authUsername', '');
-      body.set('authPassword', '');
-      fetch('?/save', {
-        method: 'POST',
-        body,
-        headers: { 'x-sveltekit-action': 'true' }
-      })
-        .then(() => {
-          catalogVersion++;
-        })
-        .catch(() => {
-          // Server-side connection could not be re-established from localStorage.
-          // Clear stale state so the user is prompted to re-enter.
-          connectionUrl = '';
-          authType = 'none';
-          authUsername = '';
-        });
-    } else if (connectionUrl && authType === 'basic') {
+      // Submitting through the form reuses the result handling of a manual save: success loads
+      // the catalogues, failure opens the form with the error so a stale URL can be corrected.
+      // Wait a tick so the inputs reflect the restored values and use:enhance is attached.
+      void tick().then(() => submitConnection());
+    } else if ($connectionForm.connectionUrl && $connectionForm.authType === 'basic') {
       // Password is not persisted; prompt the user to re-enter credentials.
       connectionOpen = true;
     }
@@ -145,50 +161,6 @@
     getOrCreateQueryRunner(tabStore.activeTabId).fetchResults();
   });
 
-  // Connection form (SuperForms).
-  const {
-    enhance: connectionEnhance,
-    errors: connectionErrors,
-    message: connectionMessage,
-    submitting: connectionSubmitting
-  } = superForm(
-    untrack(() => data.connectionForm),
-    {
-      onSubmit({ cancel }) {
-        const result = ConnectionSchema.safeParse({
-          connectionUrl,
-          authType,
-          authUsername,
-          authPassword
-        });
-        if (!result.success) {
-          const errors: Record<string, string[]> = {};
-          for (const issue of result.error.issues) {
-            const key = String(issue.path[0]);
-            (errors[key] ??= []).push(issue.message);
-          }
-          $connectionErrors = {
-            connectionUrl: errors.connectionUrl,
-            authType: errors.authType,
-            authUsername: errors.authUsername,
-            authPassword: errors.authPassword
-          };
-          cancel();
-        }
-      },
-      onUpdated({ form }) {
-        const msg = form.message as ConnectionMessage | undefined;
-        if (msg?.type === 'success') {
-          // Results belong to the previous connection; the server has cleared them too.
-          resetAllQueryRunners();
-          catalogVersion++;
-        } else if (msg?.type === 'error') {
-          connectionOpen = true;
-        }
-      }
-    }
-  );
-
   const isActive = $derived(runner.state !== 'IDLE' && !isTerminal(runner.state));
   const skippedStatements = $derived.by(() => {
     if (isActive || !runner.scriptProgress) return 0;
@@ -199,9 +171,9 @@
   // Password is intentionally excluded -- credentials should not be stored client-side.
   $effect(() => {
     if (!hydrated || data.trinoConfigured) return;
-    localStorage.setItem('trino_url', connectionUrl);
-    localStorage.setItem('trino_auth_type', authType);
-    localStorage.setItem('trino_username', authUsername);
+    localStorage.setItem('trino_url', $connectionForm.connectionUrl);
+    localStorage.setItem('trino_auth_type', $connectionForm.authType);
+    localStorage.setItem('trino_username', $connectionForm.authUsername);
   });
 
   // Persist settings.
@@ -244,8 +216,9 @@
   });
 
   const connectionSummary = $derived.by(() => {
-    const host = connectionUrl ? connectionUrl.replace(/^https?:\/\//, '').replace(/\/$/, '') : '-';
-    const auth = authType === 'basic' ? m.trino_auth_basic() : m.trino_auth_none();
+    const url = $connectionForm.connectionUrl;
+    const host = url ? url.replace(/^https?:\/\//, '').replace(/\/$/, '') : '-';
+    const auth = $connectionForm.authType === 'basic' ? m.trino_auth_basic() : m.trino_auth_none();
     return `${host} \u00b7 ${auth}`;
   });
 
@@ -495,12 +468,7 @@
   <div class="flex min-w-0 flex-1 flex-col">
     <!-- Connection config form (hidden when Trino is env-configured) -->
     {#if !data.trinoConfigured}
-      <form method="POST" action="?/save" use:connectionEnhance class="px-2 pt-1">
-        <input type="hidden" name="connectionUrl" value={connectionUrl} />
-        <input type="hidden" name="authType" value={authType} />
-        <input type="hidden" name="authUsername" value={authUsername} />
-        <input type="hidden" name="authPassword" value={authPassword} />
-
+      <form method="POST" action="?/save" use:connectionEnhance class="pt-1">
         <div class="border-base-300 bg-base-100 collapse rounded-xl border">
           <input
             type="checkbox"
@@ -525,11 +493,12 @@
               </label>
               <input
                 id="{uid}-conn-url"
+                name="connectionUrl"
                 type="url"
                 class="input input-sm w-full font-mono"
                 class:input-error={$connectionErrors.connectionUrl}
                 placeholder={m.trino_connection_url_placeholder()}
-                bind:value={connectionUrl}
+                bind:value={$connectionForm.connectionUrl}
               />
               {#if $connectionErrors.connectionUrl}
                 <p class="text-error text-xs">{$connectionErrors.connectionUrl}</p>
@@ -544,25 +513,25 @@
                   id="{uid}-auth-none"
                   class="btn join-item btn-sm"
                   type="radio"
-                  name="{uid}-auth"
+                  name="authType"
                   aria-label={m.trino_auth_none()}
                   value="none"
-                  bind:group={authType}
+                  bind:group={$connectionForm.authType}
                 />
                 <input
                   id="{uid}-auth-basic"
                   class="btn join-item btn-sm"
                   type="radio"
-                  name="{uid}-auth"
+                  name="authType"
                   aria-label={m.trino_auth_basic()}
                   value="basic"
-                  bind:group={authType}
+                  bind:group={$connectionForm.authType}
                 />
               </div>
             </div>
 
             <!-- Basic auth credentials -->
-            {#if authType === 'basic'}
+            {#if $connectionForm.authType === 'basic'}
               <div
                 class="
                   grid grid-cols-1 gap-3
@@ -575,11 +544,12 @@
                   </label>
                   <input
                     id="{uid}-auth-username"
+                    name="authUsername"
                     type="text"
                     class="input input-sm font-mono"
                     class:input-error={$connectionErrors.authUsername}
                     autocomplete="username"
-                    bind:value={authUsername}
+                    bind:value={$connectionForm.authUsername}
                   />
                   {#if $connectionErrors.authUsername}
                     <p class="text-error text-xs">{$connectionErrors.authUsername}</p>
@@ -591,11 +561,12 @@
                   </label>
                   <input
                     id="{uid}-auth-password"
+                    name="authPassword"
                     type="password"
                     class="input input-sm font-mono"
                     class:input-error={$connectionErrors.authPassword}
                     autocomplete="current-password"
-                    bind:value={authPassword}
+                    bind:value={$connectionForm.authPassword}
                   />
                   {#if $connectionErrors.authPassword}
                     <p class="text-error text-xs">{$connectionErrors.authPassword}</p>
diff --git a/src/routes/(app)/trino/validation.ts b/src/routes/(app)/trino/validation.ts
index eda60cbe..43d1eefb 100644
--- a/src/routes/(app)/trino/validation.ts
+++ b/src/routes/(app)/trino/validation.ts
@@ -1,4 +1,5 @@
 import { z } from 'zod';
+import * as m from '$lib/paraglide/messages.js';
 
 export { isPageSize, type PageSize } from '$lib/types/pagination.js';
 
@@ -6,7 +7,7 @@ export const TabIdSchema = z.uuid();
 
 export const ConnectionSchema = z
   .object({
-    connectionUrl: z.string().url(),
+    connectionUrl: z.url({ error: () => m.trino_connection_url_invalid() }),
     authType: z.enum(['none', 'basic']).default('none'),
     authUsername: z.string().default(''),
     authPassword: z.string().default('')
@@ -15,16 +16,16 @@ export const ConnectionSchema = z
     if (data.authType === 'basic') {
       if (!data.authUsername) {
         ctx.addIssue({
-          code: z.ZodIssueCode.custom,
+          code: 'custom',
           path: ['authUsername'],
-          message: 'Username is required for basic authentication'
+          message: m.trino_auth_username_required()
         });
       }
       if (!data.authPassword) {
         ctx.addIssue({
-          code: z.ZodIssueCode.custom,
+          code: 'custom',
           path: ['authPassword'],
-          message: 'Password is required for basic authentication'
+          message: m.trino_auth_password_required()
         });
       }
     }