feat(KB-119): add configurable thinking effort level

- Add defaultThinkingLevel to core Settings types and exports
- Thread thinking level through engine executor, merger, reviewer, triage, and pi
- Add effort dropdown to Model settings UI in SettingsModal
- Add tests for thinking effort dropdown in SettingsModal

packages/engine/src/executor.ts

@@ -352,6 +352,7 @@ export class TaskExecutor {
           onToolStart: agentLogger.onToolStart,
           defaultProvider: settings.defaultProvider,
           defaultModelId: settings.defaultModelId,
+          defaultThinkingLevel: settings.defaultThinkingLevel,
         });
 
         // Register session so the pause listener can terminate it
@@ -542,6 +543,7 @@ export class TaskExecutor {
               onText: (delta) => options.onAgentText?.(taskId, delta),
               defaultProvider: settings.defaultProvider,
               defaultModelId: settings.defaultModelId,
+              defaultThinkingLevel: settings.defaultThinkingLevel,
             },
           );
 

packages/engine/src/merger.ts

@@ -239,6 +239,7 @@ export async function aiMergeTask(
     onToolStart: agentLogger.onToolStart,
     defaultProvider: settings.defaultProvider,
     defaultModelId: settings.defaultModelId,
+    defaultThinkingLevel: settings.defaultThinkingLevel,
   });
 
   try {

packages/engine/src/pi.ts

@@ -34,6 +34,8 @@ export interface AgentOptions {
   defaultProvider?: string;
   /** Default model ID within the provider (e.g. "claude-sonnet-4-5"). Used with `defaultProvider`. */
   defaultModelId?: string;
+  /** Default thinking effort level (e.g. "medium", "high"). When provided, sets the session's thinking level after creation. */
+  defaultThinkingLevel?: string;
 }
 
 /**
@@ -79,6 +81,11 @@ export async function createKbAgent(options: AgentOptions): Promise<AgentResult>
     ...(selectedModel ? { model: selectedModel } : {}),
   });
 
+  // Apply thinking level if specified
+  if (options.defaultThinkingLevel) {
+    session.setThinkingLevel(options.defaultThinkingLevel as any);
+  }
+
   // Wire up event listeners
   session.subscribe((event) => {
     if (event.type === "message_update" && event.assistantMessageEvent.type === "text_delta") {

packages/engine/src/reviewer.ts

@@ -115,6 +115,8 @@ export interface ReviewOptions {
   defaultProvider?: string;
   /** Default model ID within the provider (e.g. "claude-sonnet-4-5"). When set with `defaultProvider`, overrides the reviewer's model selection. */
   defaultModelId?: string;
+  /** Default thinking effort level for the reviewer agent session. */
+  defaultThinkingLevel?: string;
 }
 
 /**
@@ -143,6 +145,7 @@ export async function reviewStep(
     onText: (delta) => options.onText?.(delta),
     defaultProvider: options.defaultProvider,
     defaultModelId: options.defaultModelId,
+    defaultThinkingLevel: options.defaultThinkingLevel,
   });
 
   let reviewText = "";

packages/engine/src/triage.ts

@@ -273,6 +273,7 @@ export class TriageProcessor {
           onToolStart: agentLogger.onToolStart,
           defaultProvider: settings.defaultProvider,
           defaultModelId: settings.defaultModelId,
+          defaultThinkingLevel: settings.defaultThinkingLevel,
         });
 
         try {