fix(agent): inject tool inventory note when tools change mid-session

Stale session history can cause the model to follow old "I can't do
that" patterns even when new tools are available. NativeAgent now tracks
a tool fingerprint and appends a system prompt note listing current
tools when the inventory changes, resetting on session reset.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/backends/native/agent.ts

@@ -52,6 +52,7 @@ export class NativeAgent {
   private _toolPolicyContext?: ToolPolicyContext;
   private _attachmentCollector?: OutboundAttachmentCollector;
   private _thinking: boolean = false;
+  private _lastToolFingerprint?: string;
 
   constructor(config: NativeAgentConfig) {
     this.modelClient = config.modelClient;
@@ -122,6 +123,19 @@ export class NativeAgent {
   private async toolLoop(): Promise<string> {
     const tools = this.toolRegistry!.filteredToAnthropicFormat(this._toolPolicyContext);
 
+    // Detect tool inventory changes to combat conversational inertia in long sessions.
+    // When tools change (e.g. new tools added between restarts), the model's prior messages
+    // saying "I can't do that" can override tool definitions. Injecting a system note fixes this.
+    const currentFingerprint = tools.map(t => t.name).sort().join(',');
+    const hasHistory = this.history.length > 1; // more than just the current user message
+    let effectiveSystem = this.systemPrompt;
+
+    if (hasHistory && this._lastToolFingerprint !== currentFingerprint) {
+      const toolNames = tools.map(t => t.name).join(', ');
+      effectiveSystem += `\n\n[Tool inventory updated — available tools: ${toolNames}. Use these tools directly; do not attempt workarounds for functionality that a tool already provides.]`;
+    }
+    this._lastToolFingerprint = currentFingerprint;
+
     // Build the loop messages from existing history.
     // These are the messages sent to the model, including any structured tool blocks.
     const loopMessages: LoopMessage[] = this.history.map(m => ({
@@ -134,7 +148,7 @@ export class NativeAgent {
       // model client will pass them through to the API which accepts structured content.
       const request = {
         messages: loopMessages as unknown as Message[],
-        system: this.systemPrompt,
+        system: effectiveSystem,
         tools,
         ...(this._thinking ? { thinking: true } : {}),
       };
@@ -221,6 +235,7 @@ export class NativeAgent {
     } else {
       this.inMemoryHistory = [];
     }
+    this._lastToolFingerprint = undefined;
     this.resetUsage();
   }