Default retrieval to 6 chunks instead of 2

chunks is a total per request, split across the attached sources, so an
agent with two sources and the default of 2 got a single chunk from each,
and its answers changed with whichever chunk won. 6 gives three per
source for about 4-5k more input tokens per retrieval turn.

Every literal default moves from 2 to 6: the request default, the
retrievers, the internal search tool, workflow agent nodes, scheduled and
headless runs, agent create/update/import, the source retrieval config and
the frontend forms. Existing agents and sources keep what they store; a
source saved with chunks=2 now counts as configured at 2, which is pinned
by a test.

Headless runs also read chunks=0 as unset (`or 2`), so an agent with
retrieval switched off retrieved anyway on scheduled runs; 0 now stays 0.

frontend/src/agents/NewAgent.tsx

@@ -135,7 +135,7 @@ export default function NewAgent({ mode }: { mode: 'new' | 'edit' | 'draft' }) {
     image: '',
     source: '',
     sources: [],
-    chunks: '2',
+    chunks: '6',
     retriever: 'classic',
     prompt_id: 'default',
     tools: [],
@@ -708,7 +708,7 @@ export default function NewAgent({ mode }: { mode: 'new' | 'edit' | 'draft' }) {
           agent_type: data.agent_type || 'classic',
           prompt_id: data.prompt_id || 'default',
           retriever: agentSourceIds.length === 0 ? 'classic' : '',
-          chunks: data.chunks || '2',
+          chunks: data.chunks || '6',
           tools: data.tools || [],
           ...serializeAgentSources(agentSourceIds, sourceDocs),
           models: agentModels,

frontend/src/agents/workflow/WorkflowBuilder.tsx

@@ -329,7 +329,7 @@ function createEmptyWorkflowAgent(): Agent {
     description: '',
     image: '',
     source: '',
-    chunks: '2',
+    chunks: '6',
     retriever: '',
     prompt_id: '',
     tools: [],

frontend/src/models/misc.ts

@@ -43,7 +43,7 @@ export type SourceGraphRetrievalConfig = {
 export type SourceRetrievalConfig = {
   retriever?: string; // default 'classic' (only option for now)
   exposure?: RetrievalExposure; // default 'prefetch'
-  chunks?: number; // top-k, default 2
+  chunks?: number; // top-k, default 6
   score_threshold?: number | null; // default null
   rephrase_query?: boolean; // default true
   prescreen?: SourcePrescreenConfig | null; // null = off

frontend/src/preferences/preferenceSlice.ts

@@ -58,7 +58,7 @@ const initialState: Preference = {
     { name: 'creative', id: 'creative', type: 'public' },
     { name: 'strict', id: 'strict', type: 'public' },
   ],
-  chunks: '2',
+  chunks: '6',
   selectedDocs: [],
   sourceDocs: null,
   conversations: {

frontend/src/settings/components/RetrievalOptions.test.tsx

@@ -16,6 +16,13 @@ const clone = (v: RetrievalOptionsValue): RetrievalOptionsValue =>
   JSON.parse(JSON.stringify(v));
 
 describe('configToOptions (lenient read)', () => {
+  it('defaults a source to 6 chunks, the backend default', () => {
+    // Equal to the backend's RetrievalConfig default, so a new upload is not
+    // read as a per-source override.
+    expect(DEFAULT_RETRIEVAL_OPTIONS.retrieval.chunks).toBe(6);
+    expect(configToOptions(undefined).retrieval.chunks).toBe(6);
+  });
+
   it('returns all defaults for an absent config', () => {
     expect(configToOptions(undefined)).toEqual(DEFAULT_RETRIEVAL_OPTIONS);
   });

frontend/src/settings/components/RetrievalOptions.tsx

@@ -84,7 +84,7 @@ export const DEFAULT_RETRIEVAL_OPTIONS: RetrievalOptionsValue = {
   retrieval: {
     retriever: 'classic',
     exposure: 'prefetch',
-    chunks: 2,
+    chunks: 6,
     score_threshold: null,
     rephrase_query: true,
     prescreen: {

frontend/src/store.ts

@@ -38,7 +38,7 @@ const preloadedState: { preference: Preference } = {
       { name: 'creative', id: 'creative', type: 'public' },
       { name: 'strict', id: 'strict', type: 'public' },
     ],
-    chunks: JSON.parse(chunks ?? '2').toString(),
+    chunks: JSON.parse(chunks ?? '6').toString(),
     selectedDocs: getStoredRecentDocs(),
     conversations: {
       data: null,