fix(translate): datasource change not persisted on save + preview column cleanup

Root cause: saveJob() used stale sourceDatasourceId (set once on load)
instead of live datasourceId (updated by ConfigTabForm via $bindable).
Since sourceDatasourceId was always truthy, the || fallback to datasourceId
never triggered — the old datasource ID was always sent to PUT.

Fixes:
- Removed dead sourceDatasourceId atom; saveJob() uses datasourceId directly
- Bound sourceTable via $bindable through ConfigTabForm; updated on select
- loadDatasourceColumns() syncs databaseDialect from Superset columns API
- saveJob() sends undefined for database_dialect="unknown" to force re-detect
- Backend: added direct_db+connection_id validation on update (mirroring create)
- Removed redundant "Язык ист." column from TranslationPreview table
- Removed unused getDetectedLang function

Tests:
- TranslationJobModel: datasourceId save mapping, dialect sync, unknown→undefined
- TranslateJobService: reject direct_db without connection_id, preserve existing

Verified: browser — translate_cross datasource persisted after save+reload,
dialect detected as "clickhouse", columns loaded (2), translation column preserved.

frontend/src/lib/components/translate/ConfigTabForm.svelte

@@ -46,6 +46,7 @@
     environments = [],
     datasourceId = $bindable(''),
     datasourceSearch = $bindable(''),
+    sourceTable = $bindable(''),
     databaseDialect = $bindable(''),
     availableColumns = [],
     virtualColumns = $bindable([]),
@@ -133,6 +134,7 @@
   /** Select a dataset from the dropdown */
   function selectDatasource(ds) {
     datasourceId = String(ds.id);
+    sourceTable = ds.table_name || '';
     datasourceSearch = `${ds.table_name} (${ds.database_name} · ${ds.database_dialect})`;
     showDatasourceDropdown = false;
     availableColumns = [];
@@ -154,6 +156,7 @@
       const response = await fetchDatasourceColumns(datasourceId, environmentId);
       availableColumns = response.columns || response || [];
       virtualColumns = response.virtual_columns || [];
+      if (response.database_dialect) databaseDialect = response.database_dialect;
     } catch {
       availableColumns = [];
       virtualColumns = [];

frontend/src/lib/components/translate/TranslationPreview.svelte

@@ -33,20 +33,6 @@
 		return lang ? (lang.final_value || lang.translated_value || '') : '';
 	}
 
-	/** Get detected language for a record */
-	function getDetectedLang(record) {
-		if (record.source_language_detected && record.source_language_detected !== 'und') {
-			return record.source_language_detected;
-		}
-		const langs = record.languages || [];
-		for (const l of langs) {
-			if (l.source_language_detected && l.source_language_detected !== 'und') {
-				return l.source_language_detected;
-			}
-		}
-		return 'und';
-	}
-
 	/** @returns {Promise<void>} */
 	async function handlePreview() {
 		uxState = 'loading';
@@ -206,7 +192,6 @@
 					<tr>
 						<th class="px-3 py-2 text-left text-xs font-medium text-text-muted uppercase w-12">#</th>
 						<th class="px-3 py-2 text-left text-xs font-medium text-text-muted uppercase">{_t.translate?.preview?.table_source}</th>
-						<th class="px-3 py-2 text-center text-xs font-medium text-text-muted uppercase w-28">{_t.translate?.preview?.detected_language}</th>
 						{#each targetLanguages as lang}
 							<th class="px-3 py-2 text-left text-xs font-medium text-text-muted uppercase min-w-[250px]">
 								<div class="flex items-center gap-1">
@@ -225,15 +210,6 @@
 									<code class="text-xs text-text whitespace-pre-wrap break-all">{row.source_sql || _t.translate?.preview?.empty_placeholder}</code>
 								</div>
 							</td>
-							<td class="px-3 py-2 text-center align-top">
-							<span class="inline-flex items-center gap-1 px-2 py-0.5 text-xs rounded-full font-mono
-								{getDetectedLang(row) !== 'und' ? 'bg-info-light text-info' : 'bg-warning-light text-warning'}">
-								{getDetectedLang(row)}
-								{#if getDetectedLang(row) === 'und'}
-									<span class="text-[10px] font-bold" title="Undetermined source language">⚠</span>
-								{/if}
-							</span>
-							</td>
 							{#each targetLanguages as lang}
 								{@const langVal = getLangValue(row, lang)}
 								<td class="px-3 py-2 align-top">

frontend/src/lib/models/TranslationJobModel.svelte.ts

@@ -41,7 +41,6 @@ export class TranslationJobModel {
   // ── Config form ───────────────────────────────────────────────
   name: string = $state('');
   description: string = $state('');
-  sourceDatasourceId: string = $state('');
   sourceTable: string = $state('');
   targetSchema: string = $state('');
   targetTable: string = $state('');
@@ -237,7 +236,6 @@ export class TranslationJobModel {
         this.existingJob = job;
         this.name = (job.name as string) || '';
         this.description = (job.description as string) || '';
-        this.sourceDatasourceId = (job.source_datasource_id as string) || '';
         this.sourceTable = (job.source_table as string) || '';
         this.translationColumn = (job.translation_column as string) || '';
         this.targetColumn = (job.target_column as string) || '';
@@ -298,9 +296,10 @@ export class TranslationJobModel {
   async loadDatasourceColumns(): Promise<void> {
     if (!this.datasourceId) return;
     try {
-      const res = await fetchDatasourceColumns<{ columns?: Record<string, unknown>[]; virtual?: Record<string, unknown>[] }>(this.datasourceId, this.environmentId);
+      const res = await fetchDatasourceColumns<{ columns?: Record<string, unknown>[]; virtual?: Record<string, unknown>[]; database_dialect?: string }>(this.datasourceId, this.environmentId);
       this.availableColumns = (res?.columns || []) as Record<string, unknown>[];
       this.virtualColumns = (res?.virtual || []) as Record<string, unknown>[];
+      if (res?.database_dialect) this.databaseDialect = res.database_dialect;
     } catch { this.availableColumns = []; this.virtualColumns = []; }
   }
 
@@ -324,7 +323,7 @@ export class TranslationJobModel {
       const payload = {
         name: this.name,
         description: this.description,
-        source_datasource_id: this.sourceDatasourceId || this.datasourceId,
+        source_datasource_id: this.datasourceId,
         source_table: this.sourceTable,
         translation_column: this.translationColumn,
         target_column: this.targetColumn || undefined,
@@ -339,7 +338,7 @@ export class TranslationJobModel {
         insert_method: this.insertMethod,
         connection_id: this.connectionId || undefined,
         disable_reasoning: this.disableReasoning,
-        database_dialect: this.databaseDialect || undefined,
+        database_dialect: this.databaseDialect && this.databaseDialect !== 'unknown' ? this.databaseDialect : undefined,
         target_schema: this.targetSchema || undefined,
         target_table: this.targetTable || undefined,
         target_database_id: this.targetDatabaseId || undefined,

frontend/src/lib/models/__tests__/TranslationJobModel.test.ts

@@ -7,6 +7,8 @@
 // @TEST_INVARIANT: disableReasoning-sent-in-save -> VERIFIED_BY: [sends disable_reasoning in save payload]
 // @TEST_INVARIANT: databaseDialect-sent-in-save -> VERIFIED_BY: [sends database_dialect in save payload]
 // @TEST_INVARIANT: datasourceSearch-populated-on-load -> VERIFIED_BY: [populates datasourceSearch on job load]
+// @TEST_INVARIANT: datasourceId-sent-in-save -> VERIFIED_BY: [uses current datasourceId as source_datasource_id]
+// @TEST_INVARIANT: datasourceColumns-dialect-sync -> VERIFIED_BY: [loadDatasourceColumns updates databaseDialect]
 // #endregion
 import { describe, it, expect, vi, beforeEach } from 'vitest';
 
@@ -169,6 +171,13 @@ describe('TranslationJobModel — field mapping invariants', () => {
       const payload = vi.mocked(api.requestApi).mock.calls[0][2] as Record<string, unknown>;
       expect(payload.database_dialect).toBeUndefined();
     });
+    it('sends database_dialect as undefined when unknown', async () => {
+      model.databaseDialect = 'unknown'; model.isNewJob = true;
+      vi.mocked(api.requestApi).mockResolvedValue({ id: JOB_ID });
+      await model.saveJob();
+      const payload = vi.mocked(api.requestApi).mock.calls[0][2] as Record<string, unknown>;
+      expect(payload.database_dialect).toBeUndefined();
+    });
     it('sends database_dialect on existing job update (PUT)', async () => {
       model.databaseDialect = 'mysql'; model.isNewJob = false; model.jobId = JOB_ID;
       vi.mocked(api.requestApi).mockResolvedValue({});
@@ -198,6 +207,20 @@ describe('TranslationJobModel — field mapping invariants', () => {
     });
   });
 
+  describe('datasourceId — save payload mapping', () => {
+    it('uses current datasourceId as source_datasource_id', async () => {
+      model.isNewJob = false;
+      model.jobId = JOB_ID;
+      model.datasourceId = 'new-datasource-id';
+      vi.mocked(api.requestApi).mockResolvedValue({ id: JOB_ID });
+
+      await model.saveJob();
+
+      const payload = vi.mocked(api.requestApi).mock.calls[0][2] as Record<string, unknown>;
+      expect(payload.source_datasource_id).toBe('new-datasource-id');
+    });
+  });
+
   // ═══════════════════════════════════════════════════════════════
   // uxState transitions during load
   // ═══════════════════════════════════════════════════════════════
@@ -713,6 +736,13 @@ describe('TranslationJobModel — Data Loading Helpers', () => {
     expect(model.virtualColumns).toEqual([]);
   });
 
+  it('loadDatasourceColumns updates databaseDialect from datasource metadata', async () => {
+    model.datasourceId = DS_ID; model.environmentId = ENV_ID;
+    vi.mocked(api.fetchApi).mockResolvedValue({ columns: [], virtual: [], database_dialect: 'clickhouse' });
+    await model.loadDatasourceColumns();
+    expect(model.databaseDialect).toBe('clickhouse');
+  });
+
   it('loadDatasourceColumns handles undefined columns/virtual response', async () => {
     model.datasourceId = DS_ID; model.environmentId = ENV_ID;
     vi.mocked(api.fetchApi).mockResolvedValue({});  // no columns/virtual fields at all

frontend/src/routes/translate/[id]/+page.svelte

@@ -163,6 +163,7 @@
         environments={m.environments}
         bind:datasourceId={m.datasourceId}
         bind:datasourceSearch={m.datasourceSearch}
+        bind:sourceTable={m.sourceTable}
         bind:databaseDialect={m.databaseDialect}
         bind:availableColumns={m.availableColumns}
         bind:virtualColumns={m.virtualColumns}