feat(FN-4135): add always-on web search with locked provider setting

Adds always-on web search capability to the research system, locking the web search provider in settings UI and updating the ResearchView to surface web search as a persistent toggle with agent tool integration, plus corresponding docs and test coverage.

Fusion-Task-Id: FN-4135

packages/core/src/__tests__/research-settings.test.ts

@@ -95,12 +95,25 @@ describe("resolveResearchSettings", () => {
     expect(resolved.searchProvider).toBe("brave");
   });
 
-  it("honors explicit legacy global search provider opt-out", () => {
+  it("forces web search on even when persisted settings disable it", () => {
     const resolved = resolveResearchSettings({
-      researchGlobalWebSearchProvider: "none",
+      researchGlobalDefaults: {
+        enabledSources: {
+          webSearch: false,
+          pageFetch: true,
+          github: false,
+          localDocs: true,
+          llmSynthesis: true,
+        },
+      },
+      researchSettings: {
+        enabledSources: {
+          webSearch: false,
+        },
+      },
     });
 
-    expect(resolved.searchProvider).toBe("none");
+    expect(resolved.enabledSources.webSearch).toBe(true);
   });
 
   it("supports null-as-delete semantics for researchSettings object", () => {

packages/core/src/research-settings.ts

@@ -22,8 +22,7 @@ export interface ResolvedResearchSettings {
 
 const DEFAULT_SEARCH_PROVIDER = "builtin";
 
-const FALLBACK_SOURCES: ResearchEnabledSources = {
-  webSearch: true,
+const FALLBACK_SOURCES: Omit<ResearchEnabledSources, "webSearch"> = {
   pageFetch: true,
   github: false,
   localDocs: true,
@@ -44,10 +43,7 @@ export function resolveResearchSettings(settings: Partial<Settings> | undefined)
     synthesisProvider: projectSettings?.synthesisProvider ?? globalDefaults?.synthesisProvider,
     synthesisModelId: projectSettings?.synthesisModelId ?? globalDefaults?.synthesisModelId,
     enabledSources: {
-      webSearch:
-        projectSettings?.enabledSources?.webSearch ??
-        globalDefaults?.enabledSources?.webSearch ??
-        FALLBACK_SOURCES.webSearch,
+      webSearch: true,
       pageFetch:
         projectSettings?.enabledSources?.pageFetch ??
         globalDefaults?.enabledSources?.pageFetch ??

packages/core/src/types.ts

@@ -1531,7 +1531,7 @@ export interface DaemonTokenSettings {
  * The dashboard UI shows these under a "Global" section.
  */
 /** Web search backend for auto-research provider. */
-export type WebSearchBackend = "builtin" | "searxng" | "brave" | "google" | "tavily" | "none";
+export type WebSearchBackend = "builtin" | "searxng" | "brave" | "google" | "tavily";
 
 export interface ResearchEnabledSources {
   webSearch: boolean;
@@ -1858,7 +1858,7 @@ export interface GlobalSettings {
   /** Default maximum number of synthesis rounds per run.
    *  Default: 2. */
   researchGlobalMaxSynthesisRounds?: number;
-  /** Web search backend for auto-research. Default: "builtin". */
+  /** Web search backend for auto-research. Default: "builtin"; web search itself cannot be disabled. */
   researchGlobalWebSearchProvider?: WebSearchBackend;
   /** SearXNG instance URL (required when researchGlobalWebSearchProvider is "searxng"). */
   researchGlobalSearxngUrl?: string;