fix(coding-agent): validate extension command registration

Reject extension commands without a non-empty string name or a handler
at registration, instead of letting them crash the editor when typing /.

fixes #10054

packages/coding-agent/CHANGELOG.md

@@ -19,6 +19,7 @@
 - Fixed codemode `image()` accepting malformed base64 data or unsupported image types, which persisted an invalid image block that made every later provider request fail with HTTP 400 ([#10215](https://github.com/earendil-works/pi/issues/10215)).
 - Fixed codemode failing to start its script worker from the standalone Windows executable ([#10204](https://github.com/earendil-works/pi/issues/10204)).
 - Fixed prompt submission slowing down with session length, because resolving the session's model selection looked up the model catalog once per assistant message ([#10198](https://github.com/earendil-works/pi/issues/10198)).
+- Fixed extension commands registered without a string name or handler crashing pi when typing `/`; the extension now fails to load with an error instead ([#10054](https://github.com/earendil-works/pi/issues/10054)).
 
 ## [0.99.1] - 2026-09-29
 

packages/coding-agent/src/core/extensions/loader.ts

@@ -301,6 +301,14 @@ function createExtensionAPI(
 
 		registerCommand(name: string, options: Omit<RegisteredCommand, "name" | "sourceInfo">): void {
 			assertActive();
+			if (typeof name !== "string" || name.length === 0) {
+				throw new Error(
+					`Command registered by extension "${extension.path}" must have a non-empty string name. Use pi.registerCommand("name", { description, handler }).`,
+				);
+			}
+			if (typeof options?.handler !== "function") {
+				throw new Error(`Command "/${name}" registered by extension "${extension.path}" must define handler().`);
+			}
 			extension.commands.set(name, {
 				name,
 				sourceInfo: extension.sourceInfo,