feat(cli): add thread poke command

Re-runs the head step's agent with a supplementary prompt and replaces
the head step (rewires new step's prev to old head's prev) instead of
appending. Skips moderator re-route — the role of the head step is
reused.

Fixes #144

packages/cli/src/cli.ts

@@ -17,6 +17,7 @@ import {
   cmdThreadCancel,
   cmdThreadExec,
   cmdThreadList,
+  cmdThreadPoke,
   cmdThreadRead,
   cmdThreadResume,
   cmdThreadShow,
@@ -290,6 +291,26 @@ thread
     });
   });
 
+thread
+  .command("poke")
+  .description("Re-run the head step's agent with a supplementary prompt (replaces head step)")
+  .argument("<thread-id>", "Thread ULID")
+  .requiredOption("-p, --prompt <text>", "Supplementary prompt for the agent")
+  .option("--agent <cmd>", "Override agent command (defaults to head step's agent)")
+  .action((threadId: string, opts: { prompt: string; agent: string | undefined }) => {
+    const storageRoot = resolveStorageRoot();
+    runAction(async () => {
+      const agentOverride = opts.agent ?? null;
+      const result = await cmdThreadPoke(
+        storageRoot,
+        threadId as ThreadId,
+        opts.prompt,
+        agentOverride,
+      );
+      writeOutput(result);
+    });
+  });
+
 thread
   .command("stop")
   .description("Stop background execution of a thread (keep thread active)")