fix(coding-agent): clamp thinking level to model capabilities

- setThinkingLevel() now clamps xhigh to high when model doesn't support it
- Model changes automatically re-clamp the current thinking level
- Fixed /model command to use session.setModel() instead of agent.setModel()
- Footer and editor border color update after model/thinking changes

Closes #253

packages/coding-agent/src/core/agent-session.ts

@@ -543,6 +543,9 @@ export class AgentSession {
 		this.agent.setModel(model);
 		this.sessionManager.saveModelChange(model.provider, model.id);
 		this.settingsManager.setDefaultModelAndProvider(model.provider, model.id);
+
+		// Re-clamp thinking level for new model's capabilities
+		this.setThinkingLevel(this.thinkingLevel);
 	}
 
 	/**
@@ -580,13 +583,10 @@ export class AgentSession {
 		this.sessionManager.saveModelChange(next.model.provider, next.model.id);
 		this.settingsManager.setDefaultModelAndProvider(next.model.provider, next.model.id);
 
-		// Apply thinking level (silently use "off" if not supported)
-		const effectiveThinking = next.model.reasoning ? next.thinkingLevel : "off";
-		this.agent.setThinkingLevel(effectiveThinking);
-		this.sessionManager.saveThinkingLevelChange(effectiveThinking);
-		this.settingsManager.setDefaultThinkingLevel(effectiveThinking);
+		// Apply thinking level (setThinkingLevel clamps to model capabilities)
+		this.setThinkingLevel(next.thinkingLevel);
 
-		return { model: next.model, thinkingLevel: effectiveThinking, isScoped: true };
+		return { model: next.model, thinkingLevel: this.thinkingLevel, isScoped: true };
 	}
 
 	private async _cycleAvailableModel(): Promise<ModelCycleResult | null> {
@@ -612,6 +612,9 @@ export class AgentSession {
 		this.sessionManager.saveModelChange(nextModel.provider, nextModel.id);
 		this.settingsManager.setDefaultModelAndProvider(nextModel.provider, nextModel.id);
 
+		// Re-clamp thinking level for new model's capabilities
+		this.setThinkingLevel(this.thinkingLevel);
+
 		return { model: nextModel, thinkingLevel: this.thinkingLevel, isScoped: false };
 	}
 
@@ -630,11 +633,16 @@ export class AgentSession {
 
 	/**
 	 * Set thinking level.
-	 * Silently uses "off" if model doesn't support thinking.
+	 * Clamps to model capabilities: "off" if no reasoning, "high" if xhigh unsupported.
 	 * Saves to session and settings.
 	 */
 	setThinkingLevel(level: ThinkingLevel): void {
-		const effectiveLevel = this.supportsThinking() ? level : "off";
+		let effectiveLevel = level;
+		if (!this.supportsThinking()) {
+			effectiveLevel = "off";
+		} else if (level === "xhigh" && !this.supportsXhighThinking()) {
+			effectiveLevel = "high";
+		}
 		this.agent.setThinkingLevel(effectiveLevel);
 		this.sessionManager.saveThinkingLevelChange(effectiveLevel);
 		this.settingsManager.setDefaultThinkingLevel(effectiveLevel);
@@ -1183,10 +1191,10 @@ export class AgentSession {
 			}
 		}
 
-		// Restore thinking level if saved
+		// Restore thinking level if saved (setThinkingLevel clamps to model capabilities)
 		const savedThinking = this.sessionManager.loadThinkingLevel();
 		if (savedThinking) {
-			this.agent.setThinkingLevel(savedThinking as ThinkingLevel);
+			this.setThinkingLevel(savedThinking as ThinkingLevel);
 		}
 
 		this._reconnectToAgent();

packages/coding-agent/src/main.ts

@@ -3,6 +3,7 @@
  */
 
 import { Agent, type Attachment, ProviderTransport, type ThinkingLevel } from "@mariozechner/pi-agent-core";
+import { supportsXhigh } from "@mariozechner/pi-ai";
 import chalk from "chalk";
 import { type Args, parseArgs, printHelp } from "./cli/args.js";
 import { processFileArguments } from "./cli/file-processor.js";
@@ -294,6 +295,15 @@ export async function main(args: string[]) {
 		initialThinking = parsed.thinking;
 	}
 
+	// Clamp thinking level to model capabilities
+	if (initialModel) {
+		if (!initialModel.reasoning) {
+			initialThinking = "off";
+		} else if (initialThinking === "xhigh" && !supportsXhigh(initialModel)) {
+			initialThinking = "high";
+		}
+	}
+
 	// Determine which tools to use
 	let selectedTools = parsed.tools ? parsed.tools.map((name) => allTools[name]) : codingTools;
 
@@ -378,11 +388,6 @@ export async function main(args: string[]) {
 		}),
 	});
 
-	// If initial thinking was requested but model doesn't support it, reset to off
-	if (initialThinking !== "off" && initialModel && !initialModel.reasoning) {
-		agent.setThinkingLevel("off");
-	}
-
 	// Load previous messages if continuing, resuming, or using --session
 	if (parsed.continue || parsed.resume || parsed.session) {
 		const messages = sessionManager.loadMessages();

packages/coding-agent/src/modes/interactive/interactive-mode.ts

@@ -1172,6 +1172,7 @@ export class InteractiveMode {
 		if (newLevel === null) {
 			this.showStatus("Current model does not support thinking");
 		} else {
+			this.footer.updateState(this.session.state);
 			this.updateEditorBorderColor();
 			this.showStatus(`Thinking level: ${newLevel}`);
 		}
@@ -1184,6 +1185,7 @@ export class InteractiveMode {
 				const msg = this.session.scopedModels.length > 0 ? "Only one model in scope" : "Only one model available";
 				this.showStatus(msg);
 			} else {
+				this.footer.updateState(this.session.state);
 				this.updateEditorBorderColor();
 				const thinkingStr =
 					result.model.reasoning && result.thinkingLevel !== "off" ? ` (thinking: ${result.thinkingLevel})` : "";
@@ -1310,6 +1312,7 @@ export class InteractiveMode {
 				this.session.getAvailableThinkingLevels(),
 				(level) => {
 					this.session.setThinkingLevel(level);
+					this.footer.updateState(this.session.state);
 					this.updateEditorBorderColor();
 					done();
 					this.showStatus(`Thinking level: ${level}`);
@@ -1379,11 +1382,17 @@ export class InteractiveMode {
 				this.ui,
 				this.session.model,
 				this.settingsManager,
-				(model) => {
-					this.agent.setModel(model);
-					this.sessionManager.saveModelChange(model.provider, model.id);
-					done();
-					this.showStatus(`Model: ${model.id}`);
+				async (model) => {
+					try {
+						await this.session.setModel(model);
+						this.footer.updateState(this.session.state);
+						this.updateEditorBorderColor();
+						done();
+						this.showStatus(`Model: ${model.id}`);
+					} catch (error) {
+						done();
+						this.showError(error instanceof Error ? error.message : String(error));
+					}
 				},
 				() => {
 					done();