feat(models): add background task model override config and runtime wiring

src/backends/native/orchestrator.ts

@@ -1,5 +1,5 @@
 import type { ModelRouter, ModelTier } from '../../models/router.js';
-import type { ChatRequest, Message, TokenUsage } from '../../models/types.js';
+import type { ChatRequest, Message, ModelClient, TokenUsage } from '../../models/types.js';
 import type { Session } from '../../session/index.js';
 import type { ToolRegistry } from '../../tools/registry.js';
 import type { ToolExecutor } from '../../tools/executor.js';
@@ -22,6 +22,7 @@ import { CONTEXT_CHECKPOINT_PROMPT, MEMORY_EXTRACTION_PROMPT } from './prompts.j
 /** A single-turn, stateless request to a sub-agent at a specific tier. */
 export interface SubAgentRequest {
   tier: ModelTier;
+  task?: keyof DelegationConfig;
   systemPrompt: string;
   message: string;
   maxTokens?: number;
@@ -106,6 +107,12 @@ export interface OrchestratorConfig {
   primaryTier: ModelTier;
   /** Which tier to use for each delegation task type. */
   delegation: DelegationConfig;
+  /** Optional direct provider/model overrides for specific delegation task types. */
+  backgroundModelOverrides?: Partial<Record<keyof DelegationConfig, {
+    client: ModelClient;
+    label: string;
+    fallbackTier: ModelTier;
+  }>>;
   /** Maximum nesting depth for delegation calls (safety guard). */
   maxDelegationDepth: number;
   onToolUse?: (event: ToolUseEvent) => void;
@@ -157,6 +164,11 @@ export class AgentOrchestrator {
   private _agent: NativeAgent;
   private _modelRouter: ModelRouter;
   private _delegation: DelegationConfig;
+  private _backgroundModelOverrides: Partial<Record<keyof DelegationConfig, {
+    client: ModelClient;
+    label: string;
+    fallbackTier: ModelTier;
+  }>>;
   private _maxDelegationDepth: number;
   private _toolRegistry?: ToolRegistry;
   private _session?: Session;
@@ -185,6 +197,7 @@ export class AgentOrchestrator {
   constructor(config: OrchestratorConfig) {
     this._modelRouter = config.modelRouter;
     this._delegation = config.delegation;
+    this._backgroundModelOverrides = config.backgroundModelOverrides ?? {};
     this._maxDelegationDepth = config.maxDelegationDepth;
     this._toolRegistry = config.toolRegistry;
     this._session = config.session;
@@ -262,6 +275,30 @@ export class AgentOrchestrator {
       chatRequest.tools = this._toolRegistry.filteredToAnthropicFormat(policyContext);
     }
 
+    const override = request.task ? this._backgroundModelOverrides[request.task] : undefined;
+    if (override) {
+      try {
+        const response = await override.client.chat(chatRequest);
+        this._trackUsage(tier, response.usage);
+        console.log(
+          `[Flynn:delegate] task=${request.task} provider_model=${override.label} fallback_tier=${override.fallbackTier} ` +
+          `tokens=${response.usage.inputTokens}+${response.usage.outputTokens}`,
+        );
+        return {
+          content: response.content,
+          usage: response.usage,
+          tier,
+        };
+      } catch (error) {
+        const message = error instanceof Error ? error.message : String(error);
+        console.warn(
+          `[Flynn:delegate] task=${request.task} provider/model override failed (${override.label}): ${message}; ` +
+          `falling back to tier='${override.fallbackTier}'`,
+        );
+        tier = override.fallbackTier;
+      }
+    }
+
     const response = await this._modelRouter.chat(chatRequest, tier);
 
     // Track cumulative usage for this tier
@@ -645,6 +682,7 @@ export class AgentOrchestrator {
     try {
       const extractionTier = this.getDelegationTier('memory_extraction');
       const extraction = await this.delegate({
+        task: 'memory_extraction',
         tier: extractionTier,
         systemPrompt: MEMORY_EXTRACTION_PROMPT,
         message: this._buildExtractionInput(userMessage, assistantText, toolCallsInRun),
@@ -861,6 +899,7 @@ export class AgentOrchestrator {
     try {
       const tier = this.getDelegationTier('compaction');
       const result = await this.delegate({
+        task: 'compaction',
         tier,
         systemPrompt: CONTEXT_CHECKPOINT_PROMPT,
         message: conversation,