fix(start-work): restore atlas handoff

Keep native /start-work resolvable on Sisyphus, but switch the work session back to Atlas when Atlas is registered. Stamp the outgoing agent with Atlas's actual list-display key so config→start-work execution resolves correctly and still falls back to Sisyphus when Atlas is unavailable.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/plugin/command-execute-before.ts

@@ -0,0 +1,39 @@
+import type { CreatedHooks } from "../create-hooks"
+
+type CommandExecuteBeforeInput = {
+  command: string
+  sessionID: string
+  arguments: string
+}
+
+type CommandExecuteBeforeOutput = {
+  parts: Array<{ type: string; text?: string; [key: string]: unknown }>
+}
+
+function hasPartsOutput(value: unknown): value is CommandExecuteBeforeOutput {
+  if (typeof value !== "object" || value === null) return false
+  const record = value as Record<string, unknown>
+  const parts = record["parts"]
+  return Array.isArray(parts)
+}
+
+export function createCommandExecuteBeforeHandler(args: {
+  hooks: CreatedHooks
+}): (
+  input: CommandExecuteBeforeInput,
+  output: CommandExecuteBeforeOutput,
+) => Promise<void> {
+  const { hooks } = args
+
+  return async (input, output): Promise<void> => {
+    await hooks.autoSlashCommand?.["command.execute.before"]?.(input, output)
+
+    if (
+      hooks.startWork
+      && input.command.toLowerCase() === "start-work"
+      && hasPartsOutput(output)
+    ) {
+      await hooks.startWork["command.execute.before"]?.(input, output)
+    }
+  }
+}