diff --git a/packages/pi-coding-agent/src/core/agent-session-renderable-tools.test.ts b/packages/pi-coding-agent/src/core/agent-session-renderable-tools.test.ts
new file mode 100644
index 000000000..51f7ae7fc
--- /dev/null
+++ b/packages/pi-coding-agent/src/core/agent-session-renderable-tools.test.ts
@@ -0,0 +1,70 @@
+import assert from "node:assert/strict";
+import { mkdtempSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { afterEach, beforeEach, describe, it } from "node:test";
+
+import { Agent } from "@gsd/pi-agent-core";
+import { Type } from "@sinclair/typebox";
+import type { ToolDefinition } from "./extensions/types.js";
+import { AgentSession } from "./agent-session.js";
+import { AuthStorage } from "./auth-storage.js";
+import { ModelRegistry } from "./model-registry.js";
+import { DefaultResourceLoader } from "./resource-loader.js";
+import { SessionManager } from "./session-manager.js";
+import { SettingsManager } from "./settings-manager.js";
+
+let testDir: string;
+
+async function createSession() {
+	const agentDir = join(testDir, "agent-home");
+	const authStorage = AuthStorage.inMemory({});
+	const modelRegistry = new ModelRegistry(authStorage, join(agentDir, "models.json"));
+	const settingsManager = SettingsManager.inMemory();
+	const resourceLoader = new DefaultResourceLoader({
+		cwd: testDir,
+		agentDir,
+		settingsManager,
+		noExtensions: true,
+		noPromptTemplates: true,
+		noThemes: true,
+	});
+	await resourceLoader.reload();
+
+	return new AgentSession({
+		agent: new Agent(),
+		sessionManager: SessionManager.inMemory(testDir),
+		settingsManager,
+		cwd: testDir,
+		resourceLoader,
+		modelRegistry,
+	});
+}
+
+describe("AgentSession renderable tool lookup", () => {
+	beforeEach(() => {
+		testDir = mkdtempSync(join(tmpdir(), "agent-session-tools-"));
+	});
+
+	afterEach(() => {
+		rmSync(testDir, { recursive: true, force: true });
+	});
+
+	it("matches registered tool definitions case-insensitively (#3780)", async () => {
+		const session = await createSession();
+		const bashDefinition = {
+			name: "bash",
+			label: "bash",
+			description: "Execute a shell command",
+			parameters: Type.Object({}),
+			execute: async () => ({ content: [], details: undefined }),
+		} satisfies ToolDefinition;
+
+		(session as any)._extensionRunner = {
+			getAllRegisteredTools: () => [{ definition: bashDefinition }],
+		};
+
+		assert.equal(session.getRenderableToolDefinition("Bash"), bashDefinition);
+		assert.equal(session.getRenderableToolDefinition("BASH"), bashDefinition);
+	});
+});
diff --git a/packages/pi-coding-agent/src/core/agent-session.ts b/packages/pi-coding-agent/src/core/agent-session.ts
index 782ecd04e..f5d6c3c35 100644
--- a/packages/pi-coding-agent/src/core/agent-session.ts
+++ b/packages/pi-coding-agent/src/core/agent-session.ts
@@ -1275,8 +1275,9 @@ export class AgentSession {
 	}
 
 	getRenderableToolDefinition(toolName: string): ToolDefinition | undefined {
+		const normalizedToolName = toolName.toLowerCase();
 		return [...this._getBuiltinToolDefinitions(), ...this._getRegisteredToolDefinitions()].find(
-			(tool) => tool.name === toolName,
+			(tool) => tool.name.toLowerCase() === normalizedToolName,
 		);
 	}