fix: WebSearch providers + MCPTool bugs (#593)

* fix: WebSearch providers + MCPTool bugs

WebSearchTool:
- custom.ts: fix buildAuthHeadersForPreset WEB_AUTH_HEADER opt-out
- custom.ts: fix WEB_AUTH_SCHEME empty string handling
- custom.ts: fix walkJsonPath null safety for jsonPath parsing
- duckduckgo.ts: use SafeSearchType enum instead of raw 0
- mojeek.ts: always send Accept: application/json header
- README: fix timeout documentation (15s -> 120s to match code)
- custom.test.ts: add tests for auth header behavior

MCPTool:
- MCPTool.ts: fix outputSchema to accept ContentBlockParam[] (not just string)
- MCPTool.ts: fix isResultTruncated for array output (iterates text blocks)

* fix: address PR #593 review feedback

1. Export buildAuthHeadersForPreset and add direct tests for:
   - WEB_AUTH_HEADER="" explicit opt-out behavior
   - WEB_AUTH_SCHEME="" stripping scheme prefix
   - Preset defaults (authHeader + authScheme)
   - No WEB_KEY returns empty headers

2. Add duckduckgo.test.ts verifying SafeSearchType.STRICT === 0,
   confirming the enum change is semantically identical to the
   previous raw value.

Addresses review by @Vasanthdev2004 at
pullrequestreview-4093533095

---------

Co-authored-by: FluxLuFFy <flux@openclaude.dev>
Co-authored-by: Fix Bot <fix@openclaude.local>

src/tools/MCPTool/MCPTool.ts

@@ -14,8 +14,21 @@ import {
 export const inputSchema = lazySchema(() => z.object({}).passthrough())
 type InputSchema = ReturnType<typeof inputSchema>
 
+// MCP tools can return either a plain string or an array of content blocks
+// (text, images, etc.). The outputSchema must reflect both shapes so the model
+// knows rich content is possible.
 export const outputSchema = lazySchema(() =>
-  z.string().describe('MCP tool execution result'),
+  z.union([
+    z.string().describe('MCP tool execution result as text'),
+    z
+      .array(
+        z.object({
+          type: z.string(),
+          text: z.string().optional(),
+        }),
+      )
+      .describe('MCP tool execution result as content blocks'),
+  ]),
 )
 type OutputSchema = ReturnType<typeof outputSchema>
 
@@ -65,7 +78,19 @@ export const MCPTool = buildTool({
   renderToolUseProgressMessage,
   renderToolResultMessage,
   isResultTruncated(output: Output): boolean {
-    return isOutputLineTruncated(output)
+    if (typeof output === 'string') {
+      return isOutputLineTruncated(output)
+    }
+    // Array of content blocks — check if any text block exceeds the display limit
+    if (Array.isArray(output)) {
+      return output.some(
+        block =>
+          block?.type === 'text' &&
+          typeof block.text === 'string' &&
+          isOutputLineTruncated(block.text),
+      )
+    }
+    return false
   },
   mapToolResultToToolResultBlockParam(content, toolUseID) {
     return {