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/agents.rs

@@ -70,6 +70,29 @@ impl std::fmt::Display for AgentStatus {
     }
 }
 
+/// Pipeline stages for automatic story advancement.
+#[derive(Debug, Clone, PartialEq)]
+pub enum PipelineStage {
+    /// Coding agents (coder-1, coder-2, etc.)
+    Coder,
+    /// QA review agent
+    Qa,
+    /// Mergemaster agent
+    Mergemaster,
+    /// Supervisors and unknown agents — no automatic advancement.
+    Other,
+}
+
+/// Determine the pipeline stage from an agent name.
+pub fn pipeline_stage(agent_name: &str) -> PipelineStage {
+    match agent_name {
+        "qa" => PipelineStage::Qa,
+        "mergemaster" => PipelineStage::Mergemaster,
+        name if name.starts_with("coder") => PipelineStage::Coder,
+        _ => PipelineStage::Other,
+    }
+}
+
 /// Report produced by an agent calling `report_completion`.
 #[derive(Debug, Serialize, Clone)]
 pub struct CompletionReport {
@@ -100,6 +123,8 @@ struct StoryAgent {
     event_log: Arc<Mutex<Vec<AgentEvent>>>,
     /// Set when the agent calls report_completion.
     completion: Option<CompletionReport>,
+    /// Project root, stored for pipeline advancement after completion.
+    project_root: Option<PathBuf>,
 }
 
 /// Build an `AgentInfo` snapshot from a `StoryAgent` map entry.
@@ -137,11 +162,14 @@ impl AgentPool {
 
     /// Start an agent for a story: load config, create worktree, spawn agent.
     /// If `agent_name` is None, defaults to the first configured agent.
+    /// If `resume_context` is provided, it is appended to the rendered prompt
+    /// so the agent can pick up from a previous failed attempt.
     pub async fn start_agent(
         &self,
         project_root: &Path,
         story_id: &str,
         agent_name: Option<&str>,
+        resume_context: Option<&str>,
     ) -> Result<AgentInfo, String> {
         let config = ProjectConfig::load(project_root)?;
 
@@ -193,6 +221,7 @@ impl AgentPool {
                     task_handle: None,
                     event_log: event_log.clone(),
                     completion: None,
+                    project_root: Some(project_root.to_path_buf()),
                 },
             );
         }
@@ -219,9 +248,14 @@ impl AgentPool {
 
         // Spawn the agent process
         let wt_path_str = wt_info.path.to_string_lossy().to_string();
-        let (command, args, prompt) =
+        let (command, args, mut prompt) =
             config.render_agent_args(&wt_path_str, story_id, Some(&resolved_name), Some(&wt_info.base_branch))?;
 
+        // Append resume context if this is a restart with failure information.
+        if let Some(ctx) = resume_context {
+            prompt.push_str(ctx);
+        }
+
         let sid = story_id.to_string();
         let aname = resolved_name.clone();
         let tx_clone = tx.clone();
@@ -495,6 +529,186 @@ impl AgentPool {
         worktree::create_worktree(project_root, story_id, &config, self.port).await
     }
 
+    /// Advance the pipeline after an agent completes.
+    ///
+    /// Called internally by `report_completion` as a background task.
+    /// Reads the stored completion report and project_root from the agent,
+    /// then drives the next pipeline stage based on the agent's role:
+    ///
+    /// - **Coder** + gates passed → move story to `work/3_qa/`, start `qa` agent.
+    /// - **Coder** + gates failed → restart the same coder agent with failure context.
+    /// - **QA** + gates passed → move story to `work/4_merge/`, start `mergemaster` agent.
+    /// - **QA** + gates failed → restart `qa` with failure context.
+    /// - **Mergemaster** → run `script/test` on master; if pass: archive + cleanup worktree;
+    ///   if fail: restart `mergemaster` with failure context.
+    /// - **Other** (supervisor, unknown) → no automatic advancement.
+    async fn run_pipeline_advance_for_completed_agent(&self, story_id: &str, agent_name: &str) {
+        let key = composite_key(story_id, agent_name);
+
+        let (completion, project_root) = {
+            let agents = match self.agents.lock() {
+                Ok(a) => a,
+                Err(e) => {
+                    eprintln!("[pipeline] Failed to lock agents for '{story_id}:{agent_name}': {e}");
+                    return;
+                }
+            };
+            let agent = match agents.get(&key) {
+                Some(a) => a,
+                None => return,
+            };
+            (agent.completion.clone(), agent.project_root.clone())
+        };
+
+        let completion = match completion {
+            Some(c) => c,
+            None => {
+                eprintln!("[pipeline] No completion report for '{story_id}:{agent_name}'");
+                return;
+            }
+        };
+        let project_root = match project_root {
+            Some(p) => p,
+            None => {
+                eprintln!("[pipeline] No project_root for '{story_id}:{agent_name}'");
+                return;
+            }
+        };
+
+        let stage = pipeline_stage(agent_name);
+
+        match stage {
+            PipelineStage::Other => {
+                // Supervisors and unknown agents do not advance the pipeline.
+            }
+            PipelineStage::Coder => {
+                if completion.gates_passed {
+                    eprintln!(
+                        "[pipeline] Coder '{agent_name}' passed gates for '{story_id}'. Moving to QA."
+                    );
+                    if let Err(e) = move_story_to_qa(&project_root, story_id) {
+                        eprintln!("[pipeline] Failed to move '{story_id}' to 3_qa/: {e}");
+                        return;
+                    }
+                    if let Err(e) = self
+                        .start_agent(&project_root, story_id, Some("qa"), None)
+                        .await
+                    {
+                        eprintln!("[pipeline] Failed to start qa agent for '{story_id}': {e}");
+                    }
+                } else {
+                    eprintln!(
+                        "[pipeline] Coder '{agent_name}' failed gates for '{story_id}'. Restarting."
+                    );
+                    let context = format!(
+                        "\n\n---\n## Previous Attempt Failed\n\
+                         The acceptance gates failed with the following output:\n{}\n\n\
+                         Please review the failures above, fix the issues, and try again.",
+                        completion.gate_output
+                    );
+                    if let Err(e) = self
+                        .start_agent(&project_root, story_id, Some(agent_name), Some(&context))
+                        .await
+                    {
+                        eprintln!(
+                            "[pipeline] Failed to restart coder '{agent_name}' for '{story_id}': {e}"
+                        );
+                    }
+                }
+            }
+            PipelineStage::Qa => {
+                if completion.gates_passed {
+                    eprintln!(
+                        "[pipeline] QA passed gates for '{story_id}'. Moving to merge."
+                    );
+                    if let Err(e) = move_story_to_merge(&project_root, story_id) {
+                        eprintln!("[pipeline] Failed to move '{story_id}' to 4_merge/: {e}");
+                        return;
+                    }
+                    if let Err(e) = self
+                        .start_agent(&project_root, story_id, Some("mergemaster"), None)
+                        .await
+                    {
+                        eprintln!("[pipeline] Failed to start mergemaster for '{story_id}': {e}");
+                    }
+                } else {
+                    eprintln!(
+                        "[pipeline] QA failed gates for '{story_id}'. Restarting."
+                    );
+                    let context = format!(
+                        "\n\n---\n## Previous QA Attempt Failed\n\
+                         The acceptance gates failed with the following output:\n{}\n\n\
+                         Please re-run and fix the issues.",
+                        completion.gate_output
+                    );
+                    if let Err(e) = self
+                        .start_agent(&project_root, story_id, Some("qa"), Some(&context))
+                        .await
+                    {
+                        eprintln!("[pipeline] Failed to restart qa for '{story_id}': {e}");
+                    }
+                }
+            }
+            PipelineStage::Mergemaster => {
+                // Run script/test on master (project_root) as the post-merge verification.
+                eprintln!(
+                    "[pipeline] Mergemaster completed for '{story_id}'. Running post-merge tests on master."
+                );
+                let root = project_root.clone();
+                let test_result = tokio::task::spawn_blocking(move || run_project_tests(&root))
+                    .await
+                    .unwrap_or_else(|e| {
+                        eprintln!("[pipeline] Post-merge test task panicked: {e}");
+                        Ok((false, format!("Test task panicked: {e}")))
+                    });
+                let (passed, output) = match test_result {
+                    Ok(pair) => pair,
+                    Err(e) => (false, e),
+                };
+
+                if passed {
+                    eprintln!(
+                        "[pipeline] Post-merge tests passed for '{story_id}'. Archiving."
+                    );
+                    if let Err(e) = move_story_to_archived(&project_root, story_id) {
+                        eprintln!("[pipeline] Failed to archive '{story_id}': {e}");
+                    }
+                    let config =
+                        crate::config::ProjectConfig::load(&project_root).unwrap_or_default();
+                    if let Err(e) =
+                        worktree::remove_worktree_by_story_id(&project_root, story_id, &config)
+                            .await
+                    {
+                        eprintln!(
+                            "[pipeline] Failed to remove worktree for '{story_id}': {e}"
+                        );
+                    }
+                    eprintln!(
+                        "[pipeline] Story '{story_id}' archived and worktree cleaned up."
+                    );
+                } else {
+                    eprintln!(
+                        "[pipeline] Post-merge tests failed for '{story_id}'. Restarting mergemaster."
+                    );
+                    let context = format!(
+                        "\n\n---\n## Post-Merge Test Failed\n\
+                         The tests on master failed with the following output:\n{}\n\n\
+                         Please investigate and resolve the failures, then call merge_agent_work again.",
+                        output
+                    );
+                    if let Err(e) = self
+                        .start_agent(&project_root, story_id, Some("mergemaster"), Some(&context))
+                        .await
+                    {
+                        eprintln!(
+                            "[pipeline] Failed to restart mergemaster for '{story_id}': {e}"
+                        );
+                    }
+                }
+            }
+        }
+    }
+
     /// Report that an agent has finished work on a story.
     ///
     /// - Rejects with an error if the worktree has uncommitted changes.
@@ -577,6 +791,21 @@ impl AgentPool {
             session_id,
         });
 
+        // Advance the pipeline state machine in a background task.
+        // Only advance when the agent completed (not failed) to avoid spurious restarts
+        // from agents that never ran acceptance gates properly.
+        let pool_clone = Self {
+            agents: Arc::clone(&self.agents),
+            port: self.port,
+        };
+        let sid = story_id.to_string();
+        let aname = agent_name.to_string();
+        tokio::spawn(async move {
+            pool_clone
+                .run_pipeline_advance_for_completed_agent(&sid, &aname)
+                .await;
+        });
+
         Ok(report)
     }
 
@@ -701,6 +930,7 @@ impl AgentPool {
                 task_handle: None,
                 event_log: Arc::new(Mutex::new(Vec::new())),
                 completion: None,
+                project_root: None,
             },
         );
         tx
@@ -734,6 +964,38 @@ impl AgentPool {
                 task_handle: None,
                 event_log: Arc::new(Mutex::new(Vec::new())),
                 completion: None,
+                project_root: None,
+            },
+        );
+        tx
+    }
+
+    /// Test helper: inject an agent with a completion report and project_root
+    /// for testing pipeline advance logic without spawning real agents.
+    #[cfg(test)]
+    pub fn inject_test_agent_with_completion(
+        &self,
+        story_id: &str,
+        agent_name: &str,
+        status: AgentStatus,
+        project_root: PathBuf,
+        completion: CompletionReport,
+    ) -> broadcast::Sender<AgentEvent> {
+        let (tx, _) = broadcast::channel::<AgentEvent>(64);
+        let key = composite_key(story_id, agent_name);
+        let mut agents = self.agents.lock().unwrap();
+        agents.insert(
+            key,
+            StoryAgent {
+                agent_name: agent_name.to_string(),
+                status,
+                worktree_info: None,
+                session_id: None,
+                tx: tx.clone(),
+                task_handle: None,
+                event_log: Arc::new(Mutex::new(Vec::new())),
+                completion: Some(completion),
+                project_root: Some(project_root),
             },
         );
         tx
@@ -861,13 +1123,14 @@ pub fn move_story_to_archived(project_root: &Path, story_id: &str) -> Result<(),
     Ok(())
 }
 
-/// Move a story/bug from `work/2_current/` to `work/4_merge/` and auto-commit.
+/// Move a story/bug from `work/2_current/` or `work/3_qa/` to `work/4_merge/`.
 ///
 /// This stages a work item as ready for the mergemaster to pick up and merge into master.
 /// Idempotent: if already in `4_merge/`, returns Ok without committing.
 pub fn move_story_to_merge(project_root: &Path, story_id: &str) -> Result<(), String> {
     let sk = project_root.join(".story_kit").join("work");
     let current_path = sk.join("2_current").join(format!("{story_id}.md"));
+    let qa_path = sk.join("3_qa").join(format!("{story_id}.md"));
     let merge_dir = sk.join("4_merge");
     let merge_path = merge_dir.join(format!("{story_id}.md"));
 
@@ -876,18 +1139,28 @@ pub fn move_story_to_merge(project_root: &Path, story_id: &str) -> Result<(), St
         return Ok(());
     }
 
-    if !current_path.exists() {
+    // Accept from 2_current/ (manual trigger) or 3_qa/ (pipeline advancement from QA stage).
+    let source_path = if current_path.exists() {
+        current_path.clone()
+    } else if qa_path.exists() {
+        qa_path.clone()
+    } else {
         return Err(format!(
-            "Work item '{story_id}' not found in work/2_current/. Cannot move to 4_merge/."
+            "Work item '{story_id}' not found in work/2_current/ or work/3_qa/. Cannot move to 4_merge/."
         ));
-    }
+    };
 
     std::fs::create_dir_all(&merge_dir)
         .map_err(|e| format!("Failed to create work/4_merge/ directory: {e}"))?;
-    std::fs::rename(&current_path, &merge_path)
+    std::fs::rename(&source_path, &merge_path)
         .map_err(|e| format!("Failed to move '{story_id}' to 4_merge/: {e}"))?;
 
-    eprintln!("[lifecycle] Moved '{story_id}' from work/2_current/ to work/4_merge/");
+    let from_dir = if source_path == current_path {
+        "work/2_current/"
+    } else {
+        "work/3_qa/"
+    };
+    eprintln!("[lifecycle] Moved '{story_id}' from {from_dir} to work/4_merge/");
 
     Ok(())
 }
@@ -1692,6 +1965,145 @@ mod tests {
         assert_eq!(item_type_from_id("1_story_simple"), "story");
     }
 
+    // ── pipeline_stage tests ──────────────────────────────────────────────────
+
+    #[test]
+    fn pipeline_stage_detects_coders() {
+        assert_eq!(pipeline_stage("coder-1"), PipelineStage::Coder);
+        assert_eq!(pipeline_stage("coder-2"), PipelineStage::Coder);
+        assert_eq!(pipeline_stage("coder-3"), PipelineStage::Coder);
+    }
+
+    #[test]
+    fn pipeline_stage_detects_qa() {
+        assert_eq!(pipeline_stage("qa"), PipelineStage::Qa);
+    }
+
+    #[test]
+    fn pipeline_stage_detects_mergemaster() {
+        assert_eq!(pipeline_stage("mergemaster"), PipelineStage::Mergemaster);
+    }
+
+    #[test]
+    fn pipeline_stage_supervisor_is_other() {
+        assert_eq!(pipeline_stage("supervisor"), PipelineStage::Other);
+        assert_eq!(pipeline_stage("default"), PipelineStage::Other);
+        assert_eq!(pipeline_stage("unknown"), PipelineStage::Other);
+    }
+
+    // ── pipeline advance tests ────────────────────────────────────────────────
+
+    #[tokio::test]
+    async fn pipeline_advance_coder_gates_pass_moves_story_to_qa() {
+        use std::fs;
+        let tmp = tempfile::tempdir().unwrap();
+        let root = tmp.path();
+
+        // Set up story in 2_current/
+        let current = root.join(".story_kit/work/2_current");
+        fs::create_dir_all(&current).unwrap();
+        fs::write(current.join("50_story_test.md"), "test").unwrap();
+
+        let pool = AgentPool::new(3001);
+        pool.inject_test_agent_with_completion(
+            "50_story_test",
+            "coder-1",
+            AgentStatus::Completed,
+            root.to_path_buf(),
+            CompletionReport {
+                summary: "done".to_string(),
+                gates_passed: true,
+                gate_output: String::new(),
+            },
+        );
+
+        // Call pipeline advance directly (bypasses background spawn for testing).
+        pool.run_pipeline_advance_for_completed_agent("50_story_test", "coder-1")
+            .await;
+
+        // Story should have moved to 3_qa/ (start_agent for qa will fail in tests but
+        // the file move happens before that).
+        assert!(
+            root.join(".story_kit/work/3_qa/50_story_test.md").exists(),
+            "story should be in 3_qa/"
+        );
+        assert!(
+            !current.join("50_story_test.md").exists(),
+            "story should not still be in 2_current/"
+        );
+    }
+
+    #[tokio::test]
+    async fn pipeline_advance_qa_gates_pass_moves_story_to_merge() {
+        use std::fs;
+        let tmp = tempfile::tempdir().unwrap();
+        let root = tmp.path();
+
+        // Set up story in 3_qa/
+        let qa_dir = root.join(".story_kit/work/3_qa");
+        fs::create_dir_all(&qa_dir).unwrap();
+        fs::write(qa_dir.join("51_story_test.md"), "test").unwrap();
+
+        let pool = AgentPool::new(3001);
+        pool.inject_test_agent_with_completion(
+            "51_story_test",
+            "qa",
+            AgentStatus::Completed,
+            root.to_path_buf(),
+            CompletionReport {
+                summary: "QA done".to_string(),
+                gates_passed: true,
+                gate_output: String::new(),
+            },
+        );
+
+        pool.run_pipeline_advance_for_completed_agent("51_story_test", "qa")
+            .await;
+
+        // Story should have moved to 4_merge/
+        assert!(
+            root.join(".story_kit/work/4_merge/51_story_test.md").exists(),
+            "story should be in 4_merge/"
+        );
+        assert!(
+            !qa_dir.join("51_story_test.md").exists(),
+            "story should not still be in 3_qa/"
+        );
+    }
+
+    #[tokio::test]
+    async fn pipeline_advance_supervisor_does_not_advance() {
+        use std::fs;
+        let tmp = tempfile::tempdir().unwrap();
+        let root = tmp.path();
+
+        let current = root.join(".story_kit/work/2_current");
+        fs::create_dir_all(&current).unwrap();
+        fs::write(current.join("52_story_test.md"), "test").unwrap();
+
+        let pool = AgentPool::new(3001);
+        pool.inject_test_agent_with_completion(
+            "52_story_test",
+            "supervisor",
+            AgentStatus::Completed,
+            root.to_path_buf(),
+            CompletionReport {
+                summary: "supervised".to_string(),
+                gates_passed: true,
+                gate_output: String::new(),
+            },
+        );
+
+        pool.run_pipeline_advance_for_completed_agent("52_story_test", "supervisor")
+            .await;
+
+        // Story should NOT have moved (supervisors don't advance pipeline)
+        assert!(
+            current.join("52_story_test.md").exists(),
+            "story should still be in 2_current/ for supervisor"
+        );
+    }
+
     // ── move_story_to_merge tests ──────────────────────────────────────────────
 
     #[test]
@@ -1709,6 +2121,21 @@ mod tests {
         assert!(root.join(".story_kit/work/4_merge/20_story_foo.md").exists());
     }
 
+    #[test]
+    fn move_story_to_merge_from_qa_dir() {
+        use std::fs;
+        let tmp = tempfile::tempdir().unwrap();
+        let root = tmp.path();
+        let qa_dir = root.join(".story_kit/work/3_qa");
+        fs::create_dir_all(&qa_dir).unwrap();
+        fs::write(qa_dir.join("40_story_test.md"), "test").unwrap();
+
+        move_story_to_merge(root, "40_story_test").unwrap();
+
+        assert!(!qa_dir.join("40_story_test.md").exists());
+        assert!(root.join(".story_kit/work/4_merge/40_story_test.md").exists());
+    }
+
     #[test]
     fn move_story_to_merge_idempotent_when_already_in_merge() {
         use std::fs;
@@ -1723,10 +2150,10 @@ mod tests {
     }
 
     #[test]
-    fn move_story_to_merge_errors_when_not_in_current() {
+    fn move_story_to_merge_errors_when_not_in_current_or_qa() {
         let tmp = tempfile::tempdir().unwrap();
         let result = move_story_to_merge(tmp.path(), "99_nonexistent");
-        assert!(result.unwrap_err().contains("not found in work/2_current/"));
+        assert!(result.unwrap_err().contains("not found in work/2_current/ or work/3_qa/"));
     }
 
     // ── move_story_to_qa tests ────────────────────────────────────────────────