fix(extensibility): added centralized session slash command discovery for extensions

- Added a shared session command helper that aggregates extension, prompt, and skill slash commands.
- Updated ACP, extension UI, runtime-init, and task executor extension contexts to return session command data instead of empty arrays.

packages/coding-agent/src/modes/acp/acp-agent.ts

@@ -49,6 +49,7 @@ import { Settings } from "../../config/settings";
 import { clearPluginRootsAndCaches, resolveActiveProjectRegistryPath } from "../../discovery/helpers";
 import type { ExtensionUIContext, ExtensionUIDialogOptions } from "../../extensibility/extensions";
 import { runExtensionCompact } from "../../extensibility/extensions/compact-handler";
+import { getSessionSlashCommands } from "../../extensibility/extensions/get-commands-handler";
 import { buildSkillPromptMessage, getSkillSlashCommandName } from "../../extensibility/skills";
 import { loadSlashCommands } from "../../extensibility/slash-commands";
 import { MCPManager } from "../../mcp/manager";
@@ -1741,7 +1742,7 @@ export class AcpAgent implements Agent {
 				getActiveTools: () => record.session.getActiveToolNames(),
 				getAllTools: () => record.session.getAllToolNames(),
 				setActiveTools: toolNames => record.session.setActiveToolsByName(toolNames),
-				getCommands: () => [],
+				getCommands: () => getSessionSlashCommands(record.session),
 				setModel: async model => {
 					const apiKey = await record.session.modelRegistry.getApiKey(model);
 					if (!apiKey) {

packages/coding-agent/src/modes/controllers/extension-ui-controller.ts

@@ -16,6 +16,7 @@ import type {
 	SendUserMessageHandler,
 	TerminalInputHandler,
 } from "../../extensibility/extensions";
+import { getSessionSlashCommands } from "../../extensibility/extensions/get-commands-handler";
 import { HookEditorComponent } from "../../modes/components/hook-editor";
 import { HookInputComponent } from "../../modes/components/hook-input";
 import { HookSelectorComponent } from "../../modes/components/hook-selector";
@@ -109,7 +110,7 @@ export class ExtensionUiController {
 			},
 			getThinkingLevel: () => this.ctx.session.thinkingLevel,
 			setThinkingLevel: level => this.ctx.session.setThinkingLevel(level),
-			getCommands: () => [],
+			getCommands: () => getSessionSlashCommands(this.ctx.session),
 			getSessionName: () => this.ctx.sessionManager.getSessionName(),
 			setSessionName: name => this.#updateSessionName(name),
 		};
@@ -349,7 +350,7 @@ export class ExtensionUiController {
 			},
 			getThinkingLevel: () => this.ctx.session.thinkingLevel,
 			setThinkingLevel: (level, persist) => this.ctx.session.setThinkingLevel(level, persist),
-			getCommands: () => [],
+			getCommands: () => getSessionSlashCommands(this.ctx.session),
 			getSessionName: () => this.ctx.sessionManager.getSessionName(),
 			setSessionName: name => this.#updateSessionName(name),
 		};

packages/coding-agent/src/modes/runtime-init.ts

@@ -7,6 +7,7 @@
  * caller-supplied hooks.
  */
 import { runExtensionCompact, runExtensionSetModel } from "../extensibility/extensions/compact-handler";
+import { getSessionSlashCommands } from "../extensibility/extensions/get-commands-handler";
 import type { ExtensionError, ExtensionUIContext } from "../extensibility/extensions/types";
 import type { AgentSession } from "../session/agent-session";
 
@@ -59,7 +60,7 @@ export async function initializeExtensions(session: AgentSession, options: Initi
 			getActiveTools: () => session.getActiveToolNames(),
 			getAllTools: () => session.getAllToolNames(),
 			setActiveTools: (toolNames: string[]) => session.setActiveToolsByName(toolNames),
-			getCommands: () => [],
+			getCommands: () => getSessionSlashCommands(session),
 			setModel: model => runExtensionSetModel(session, model),
 			getThinkingLevel: () => session.thinkingLevel,
 			setThinkingLevel: level => session.setThinkingLevel(level),