refactor(core): F2 PR A R9 — McpClientManager options-object ctor

R9 (filed as F2 follow-up from #4336 review): 7 positional ctor args
collapse to (config, toolRegistry, options?: McpClientManagerOptions).
The trailing 5 (eventEmitter, sendSdkMcpMessage, healthConfig,
budgetConfig, pool) become named fields on `McpClientManagerOptions`.
Test factory `mkManager(overrides?)` introduced at the top of
`mcp-client-manager.test.ts` so each of the prior 80 inline
constructions becomes a single line naming only the field(s) the test
overrides; the 4 `undefined` sentinels each test threaded through to
reach the trailing `pool` arg are gone.

Net: 113 LOC removed (test) + 35 LOC added (src exposes interface +
mkManager factory + tool-registry call site update). Behavior
unchanged — same field assignments, same downgrade-enforce-without-
budget breadcrumb, same budget event wiring.

Filed bucket: F2 perf / cleanup PR A (R9 + W11 + W12 + R10/R23 T7),
see issue #4175 item 7 "F2 post-merge cleanup PRs". This is the first
of the 4 fixes in PR A; W11/W12/R10 follow as separate commits.

Test sweep: 84/84 mcp-client-manager.test.ts pass; typecheck clean.

packages/core/src/tools/mcp-client-manager.ts

@@ -343,6 +343,26 @@ function readBudgetFromEnv(): McpBudgetConfig {
   return { clientBudget, budgetMode };
 }
 
+/**
+ * F2 (#4175 commit 6 review fix — wenshao R9 / PR A): options bag for
+ * `McpClientManager` construction, replacing the prior 5 trailing
+ * positional parameters (`eventEmitter`, `sendSdkMcpMessage`,
+ * `healthConfig`, `budgetConfig`, `pool`). Pre-fix every test site
+ * threaded 4 explicit `undefined`s to reach the trailing `pool` arg —
+ * the fixed positions also blocked future option additions without
+ * re-ordering. The options-object form lets each caller name only the
+ * fields it cares about and keeps the constructor signature stable
+ * across future additions (e.g. when the W8 health-monitor wire-up
+ * lands a new `reconnectStrategy` knob).
+ */
+export interface McpClientManagerOptions {
+  eventEmitter?: EventEmitter;
+  sendSdkMcpMessage?: SendSdkMcpMessage;
+  healthConfig?: Partial<MCPHealthMonitorConfig>;
+  budgetConfig?: McpBudgetConfig;
+  pool?: import('./mcp-transport-pool.js').McpTransportPool;
+}
+
 /**
  * Manages the lifecycle of multiple MCP clients, including local child processes.
  * This class is responsible for starting, stopping, and discovering tools from
@@ -513,19 +533,16 @@ export class McpClientManager {
   constructor(
     config: Config,
     toolRegistry: ToolRegistry,
-    eventEmitter?: EventEmitter,
-    sendSdkMcpMessage?: SendSdkMcpMessage,
-    healthConfig?: Partial<MCPHealthMonitorConfig>,
-    budgetConfig?: McpBudgetConfig,
-    pool?: import('./mcp-transport-pool.js').McpTransportPool,
+    options: McpClientManagerOptions = {},
   ) {
     this.cliConfig = config;
     this.toolRegistry = toolRegistry;
-    this.pool = pool;
+    this.pool = options.pool;
 
-    this.eventEmitter = eventEmitter;
-    this.sendSdkMcpMessage = sendSdkMcpMessage;
-    this.healthConfig = { ...DEFAULT_HEALTH_CONFIG, ...healthConfig };
+    this.eventEmitter = options.eventEmitter;
+    this.sendSdkMcpMessage = options.sendSdkMcpMessage;
+    this.healthConfig = { ...DEFAULT_HEALTH_CONFIG, ...options.healthConfig };
+    const budgetConfig = options.budgetConfig;
 
     // Tests inject `budgetConfig` directly; production reads env vars
     // set by `qwen serve --mcp-client-budget=N --mcp-budget-mode=X`

packages/core/src/tools/tool-registry.ts

@@ -196,21 +196,19 @@ export class ToolRegistry {
     sendSdkMcpMessage?: SendSdkMcpMessage,
   ) {
     this.config = config;
-    this.mcpClientManager = new McpClientManager(
-      this.config,
-      this,
+    // F2 (#4175 commit 6 review fix — wenshao R9 / PR A): options-bag
+    // ctor; previously 7 positional args with `undefined, undefined`
+    // sentinels for `healthConfig` / `budgetConfig`. `pool` is
+    // forwarded from Config (set by daemon-mode QwenAgent in
+    // `newSessionConfig`); when undefined the manager keeps its pre-F2
+    // per-session spawn behavior, when defined non-SDK MCP discovery
+    // goes through `pool.acquire` so N sessions in the same workspace
+    // share one transport per unique server config.
+    this.mcpClientManager = new McpClientManager(this.config, this, {
       eventEmitter,
       sendSdkMcpMessage,
-      // F2 (#4175 commit 4): forward the workspace-shared MCP transport
-      // pool from Config (set by daemon-mode QwenAgent in
-      // newSessionConfig). When undefined, McpClientManager keeps its
-      // pre-F2 per-session spawn behavior. When defined, non-SDK MCP
-      // discovery goes through pool.acquire so N sessions in the same
-      // workspace share one transport per unique server config.
-      undefined, // healthConfig: keep manager defaults
-      undefined, // budgetConfig: keep manager defaults
-      this.config.getMcpTransportPool(),
-    );
+      pool: this.config.getMcpTransportPool(),
+    });
   }
 
   /**