Server drives pipeline as state machine

On agent completion, the server automatically runs script/test and
advances stories through the pipeline: coder → qa → mergemaster →
archive. Failed gates restart the agent with failure context. Agents
no longer need to call pipeline-advancing MCP tools.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/http/agents.rs

@@ -86,6 +86,7 @@ impl AgentsApi {
                 &project_root,
                 &payload.0.story_id,
                 payload.0.agent_name.as_deref(),
+                None,
             )
             .await
             .map_err(bad_request)?;