diff --git a/.story_kit/project.toml b/.story_kit/project.toml
index b7ab2c0..ce3cb3e 100644
--- a/.story_kit/project.toml
+++ b/.story_kit/project.toml
@@ -74,3 +74,27 @@ max_turns = 50
 max_budget_usd = 5.00
 prompt = "You are working in a git worktree on story {{story_id}}. Read CLAUDE.md first, then .story_kit/README.md to understand the dev process. Pick up the story from .story_kit/work/ - move it to work/2_current/ if needed. Follow the SDTW process through implementation and verification (Steps 1-3). The worktree and feature branch already exist - do not create them. Check .mcp.json for MCP tools. Do NOT accept the story or merge - commit your work and stop. If the user asks to review your changes, tell them to run: cd \"{{worktree_path}}\" && git difftool {{base_branch}}...HEAD\n\nIMPORTANT: When all your work is committed, call report_completion as your FINAL action: report_completion(story_id='{{story_id}}', agent_name='{{agent_name}}', summary='<brief summary of what you implemented>'). The server will run cargo clippy and tests automatically to verify your work."
 system_prompt = "You are a full-stack engineer working autonomously in a git worktree. Follow the Story-Driven Test Workflow strictly. Run cargo clippy and biome checks before considering work complete. Commit all your work before finishing - use a descriptive commit message. Do not accept stories, move them to archived, or merge to master - a human will do that. Do not coordinate with other agents - focus on your assigned story. ALWAYS call report_completion as your absolute final action after committing."
+
+[[agent]]
+name = "mergemaster"
+role = "Merges completed coder work into master, runs quality gates, archives stories, and cleans up worktrees."
+model = "sonnet"
+max_turns = 30
+max_budget_usd = 3.00
+prompt = """You are the mergemaster agent for story {{story_id}}. Your job is to merge the completed coder work into master using the merge_agent_work MCP tool.
+
+Read CLAUDE.md first, then .story_kit/README.md to understand the dev process.
+
+## Your Workflow
+1. Call merge_agent_work(story_id='{{story_id}}') via the MCP tool to trigger the full merge pipeline
+2. Review the result: check success, had_conflicts, gates_passed, and gate_output
+3. If merge succeeded and gates passed: report success to the human
+4. If conflicts were found: report the conflict details so the human can resolve them
+5. If gates failed after merge: report the failing output so a coder can fix it
+
+## Rules
+- Do NOT implement code yourself
+- Do NOT resolve complex conflicts yourself - report them clearly
+- Your job is to trigger the merge pipeline and report results
+- Call report_completion as your final action with a summary of what happened"""
+system_prompt = "You are the mergemaster agent. Your sole responsibility is to trigger the merge_agent_work MCP tool and report the results. Do not write code. Do not resolve conflicts manually. Report success or failure clearly so the human can act."
diff --git a/server/src/agents.rs b/server/src/agents.rs
index fa3b338..1b8d330 100644
--- a/server/src/agents.rs
+++ b/server/src/agents.rs
@@ -580,6 +580,90 @@ impl AgentPool {
         Ok(report)
     }
 
+    /// Run the full mergemaster pipeline for a completed story:
+    ///
+    /// 1. Squash-merge the story's feature branch into the current branch (master).
+    /// 2. If conflicts are found: abort the merge and report them.
+    /// 3. If the merge succeeds: run quality gates (cargo clippy + tests + pnpm).
+    /// 4. If all gates pass: archive the story and clean up the worktree.
+    ///
+    /// Returns a `MergeReport` with full details of what happened.
+    pub async fn merge_agent_work(
+        &self,
+        project_root: &Path,
+        story_id: &str,
+    ) -> Result<MergeReport, String> {
+        let branch = format!("feature/story-{story_id}");
+        let wt_path = worktree::worktree_path(project_root, story_id);
+        let root = project_root.to_path_buf();
+        let sid = story_id.to_string();
+        let br = branch.clone();
+
+        // Run blocking operations (git + cargo) off the async runtime.
+        let (merge_success, had_conflicts, conflict_details, merge_output) =
+            tokio::task::spawn_blocking(move || run_squash_merge(&root, &br, &sid))
+                .await
+                .map_err(|e| format!("Merge task panicked: {e}"))??;
+
+        if !merge_success {
+            return Ok(MergeReport {
+                story_id: story_id.to_string(),
+                success: false,
+                had_conflicts,
+                conflict_details,
+                gates_passed: false,
+                gate_output: merge_output,
+                worktree_cleaned_up: false,
+                story_archived: false,
+            });
+        }
+
+        // Merge succeeded — run quality gates in the project root.
+        let root2 = project_root.to_path_buf();
+        let (gates_passed, gate_output) =
+            tokio::task::spawn_blocking(move || run_merge_quality_gates(&root2))
+                .await
+                .map_err(|e| format!("Gate check task panicked: {e}"))??;
+
+        if !gates_passed {
+            return Ok(MergeReport {
+                story_id: story_id.to_string(),
+                success: true,
+                had_conflicts: false,
+                conflict_details: None,
+                gates_passed: false,
+                gate_output,
+                worktree_cleaned_up: false,
+                story_archived: false,
+            });
+        }
+
+        // Gates passed — archive the story.
+        let story_archived = move_story_to_archived(project_root, story_id).is_ok();
+
+        // Clean up the worktree if it exists.
+        let worktree_cleaned_up = if wt_path.exists() {
+            let config = crate::config::ProjectConfig::load(project_root)
+                .unwrap_or_default();
+            worktree::remove_worktree_by_story_id(project_root, story_id, &config)
+                .await
+                .is_ok()
+        } else {
+            false
+        };
+
+        Ok(MergeReport {
+            story_id: story_id.to_string(),
+            success: true,
+            had_conflicts: false,
+            conflict_details: None,
+            gates_passed: true,
+            gate_output,
+            worktree_cleaned_up,
+            story_archived,
+        })
+    }
+
     /// Return the port this server is running on.
     #[allow(dead_code)]
     pub fn port(&self) -> u16 {
@@ -656,6 +740,19 @@ impl AgentPool {
     }
 }
 
+/// Result of a mergemaster merge operation.
+#[derive(Debug, Serialize, Clone)]
+pub struct MergeReport {
+    pub story_id: String,
+    pub success: bool,
+    pub had_conflicts: bool,
+    pub conflict_details: Option<String>,
+    pub gates_passed: bool,
+    pub gate_output: String,
+    pub worktree_cleaned_up: bool,
+    pub story_archived: bool,
+}
+
 /// Stage one or more file paths and create a deterministic commit in the given git root.
 ///
 /// Pass deleted paths too so git stages their removal alongside any new files.
@@ -694,6 +791,7 @@ pub fn git_stage_and_commit(
 
 /// Determine the work item type from its ID (new naming: `{N}_{type}_{slug}`).
 /// Returns "bug", "spike", or "story".
+#[allow(dead_code)]
 fn item_type_from_id(item_id: &str) -> &'static str {
     // New format: {digits}_{type}_{slug}
     let after_num = item_id.trim_start_matches(|c: char| c.is_ascii_digit());
@@ -763,11 +861,13 @@ pub fn move_story_to_current(project_root: &Path, story_id: &str) -> Result<(),
 /// Move a story from `work/2_current/` to `work/5_archived/` and auto-commit.
 ///
 /// * If the story is in `2_current/`, it is moved to `5_archived/` and committed.
+/// * If the story is in `4_merge/`, it is moved to `5_archived/` and committed.
 /// * If the story is already in `5_archived/`, this is a no-op (idempotent).
-/// * If the story is not found in `2_current/` or `5_archived/`, an error is returned.
+/// * If the story is not found in `2_current/`, `4_merge/`, or `5_archived/`, an error is returned.
 pub fn move_story_to_archived(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 merge_path = sk.join("4_merge").join(format!("{story_id}.md"));
     let archived_dir = sk.join("5_archived");
     let archived_path = archived_dir.join(format!("{story_id}.md"));
 
@@ -776,25 +876,71 @@ pub fn move_story_to_archived(project_root: &Path, story_id: &str) -> Result<(),
         return Ok(());
     }
 
-    if current_path.exists() {
-        std::fs::create_dir_all(&archived_dir)
-            .map_err(|e| format!("Failed to create work/5_archived/ directory: {e}"))?;
-        std::fs::rename(&current_path, &archived_path)
-            .map_err(|e| format!("Failed to move story '{story_id}' to 5_archived/: {e}"))?;
-        eprintln!("[lifecycle] Moved story '{story_id}' from work/2_current/ to work/5_archived/");
+    // Check 2_current/ first, then 4_merge/
+    let source_path = if current_path.exists() {
+        current_path.clone()
+    } else if merge_path.exists() {
+        merge_path.clone()
+    } else {
+        return Err(format!(
+            "Story '{story_id}' not found in work/2_current/ or work/4_merge/. Cannot accept story."
+        ));
+    };
 
-        let msg = format!("story-kit: accept story {story_id}");
-        git_stage_and_commit(
-            project_root,
-            &[archived_path.as_path(), current_path.as_path()],
-            &msg,
-        )?;
+    std::fs::create_dir_all(&archived_dir)
+        .map_err(|e| format!("Failed to create work/5_archived/ directory: {e}"))?;
+    std::fs::rename(&source_path, &archived_path)
+        .map_err(|e| format!("Failed to move story '{story_id}' to 5_archived/: {e}"))?;
+
+    let from_dir = if source_path == current_path {
+        "work/2_current/"
+    } else {
+        "work/4_merge/"
+    };
+    eprintln!("[lifecycle] Moved story '{story_id}' from {from_dir} to work/5_archived/");
+
+    let msg = format!("story-kit: accept story {story_id}");
+    git_stage_and_commit(
+        project_root,
+        &[archived_path.as_path(), source_path.as_path()],
+        &msg,
+    )
+}
+
+/// Move a story/bug from `work/2_current/` to `work/4_merge/` and auto-commit.
+///
+/// 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 merge_dir = sk.join("4_merge");
+    let merge_path = merge_dir.join(format!("{story_id}.md"));
+
+    if merge_path.exists() {
+        // Already in 4_merge/ — idempotent, nothing to do.
         return Ok(());
     }
 
-    Err(format!(
-        "Story '{story_id}' not found in work/2_current/. Cannot accept story."
-    ))
+    if !current_path.exists() {
+        return Err(format!(
+            "Work item '{story_id}' not found in work/2_current/. 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)
+        .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 msg = format!("story-kit: queue {story_id} for merge");
+    git_stage_and_commit(
+        project_root,
+        &[merge_path.as_path(), current_path.as_path()],
+        &msg,
+    )
 }
 
 /// Move a bug from `work/2_current/` or `work/1_upcoming/` to `work/5_archived/` and auto-commit.
@@ -932,6 +1078,187 @@ fn run_acceptance_gates(path: &Path) -> Result<(bool, String), String> {
     Ok((all_passed, all_output))
 }
 
+// ── Mergemaster helpers ───────────────────────────────────────────────────────
+
+/// Squash-merge a feature branch into the current branch in the project root.
+///
+/// Returns `(success, had_conflicts, conflict_details, output)`.
+fn run_squash_merge(
+    project_root: &Path,
+    branch: &str,
+    story_id: &str,
+) -> Result<(bool, bool, Option<String>, String), String> {
+    let mut all_output = String::new();
+
+    // ── git merge --squash ────────────────────────────────────────
+    all_output.push_str(&format!("=== git merge --squash {branch} ===\n"));
+    let merge = Command::new("git")
+        .args(["merge", "--squash", branch])
+        .current_dir(project_root)
+        .output()
+        .map_err(|e| format!("Failed to run git merge: {e}"))?;
+
+    let merge_stdout = String::from_utf8_lossy(&merge.stdout).to_string();
+    let merge_stderr = String::from_utf8_lossy(&merge.stderr).to_string();
+    all_output.push_str(&merge_stdout);
+    all_output.push_str(&merge_stderr);
+    all_output.push('\n');
+
+    if !merge.status.success() {
+        // Conflicts detected — abort the merge and report.
+        let conflict_details = format!(
+            "Merge conflicts in branch '{branch}':\n{merge_stdout}{merge_stderr}"
+        );
+
+        // Abort the merge to restore clean state.
+        let _ = Command::new("git")
+            .args(["merge", "--abort"])
+            .current_dir(project_root)
+            .output();
+
+        all_output.push_str("=== Merge aborted due to conflicts ===\n");
+        return Ok((false, true, Some(conflict_details), all_output));
+    }
+
+    // ── git commit ─────────────────────────────────────────────
+    all_output.push_str("=== git commit ===\n");
+    let commit_msg = format!("story-kit: merge {story_id}");
+    let commit = Command::new("git")
+        .args(["commit", "-m", &commit_msg])
+        .current_dir(project_root)
+        .output()
+        .map_err(|e| format!("Failed to run git commit: {e}"))?;
+
+    let commit_stdout = String::from_utf8_lossy(&commit.stdout).to_string();
+    let commit_stderr = String::from_utf8_lossy(&commit.stderr).to_string();
+    all_output.push_str(&commit_stdout);
+    all_output.push_str(&commit_stderr);
+    all_output.push('\n');
+
+    if !commit.status.success() {
+        // Nothing to commit (e.g. empty diff) — treat as success.
+        if commit_stderr.contains("nothing to commit")
+            || commit_stdout.contains("nothing to commit")
+        {
+            return Ok((true, false, None, all_output));
+        }
+        return Ok((false, false, None, all_output));
+    }
+
+    Ok((true, false, None, all_output))
+}
+
+/// Run quality gates in the project root after a successful merge.
+///
+/// Runs: cargo clippy, cargo nextest run / cargo test, and pnpm gates if frontend/ exists.
+/// Returns `(gates_passed, combined_output)`.
+fn run_merge_quality_gates(project_root: &Path) -> Result<(bool, String), String> {
+    let mut all_output = String::new();
+    let mut all_passed = true;
+
+    // ── cargo clippy ──────────────────────────────────────────────
+    let clippy = Command::new("cargo")
+        .args(["clippy", "--all-targets", "--all-features"])
+        .current_dir(project_root)
+        .output()
+        .map_err(|e| format!("Failed to run cargo clippy: {e}"))?;
+
+    all_output.push_str("=== cargo clippy ===\n");
+    let clippy_out = format!(
+        "{}{}",
+        String::from_utf8_lossy(&clippy.stdout),
+        String::from_utf8_lossy(&clippy.stderr)
+    );
+    all_output.push_str(&clippy_out);
+    all_output.push('\n');
+
+    if !clippy.status.success() {
+        all_passed = false;
+    }
+
+    // ── cargo nextest run (fallback: cargo test) ──────────────────
+    all_output.push_str("=== tests ===\n");
+
+    let (test_success, test_out) = match Command::new("cargo")
+        .args(["nextest", "run"])
+        .current_dir(project_root)
+        .output()
+    {
+        Ok(o) => {
+            let combined = format!(
+                "{}{}",
+                String::from_utf8_lossy(&o.stdout),
+                String::from_utf8_lossy(&o.stderr)
+            );
+            (o.status.success(), combined)
+        }
+        Err(_) => {
+            let o = Command::new("cargo")
+                .args(["test"])
+                .current_dir(project_root)
+                .output()
+                .map_err(|e| format!("Failed to run cargo test: {e}"))?;
+            let combined = format!(
+                "{}{}",
+                String::from_utf8_lossy(&o.stdout),
+                String::from_utf8_lossy(&o.stderr)
+            );
+            (o.status.success(), combined)
+        }
+    };
+
+    all_output.push_str(&test_out);
+    all_output.push('\n');
+
+    if !test_success {
+        all_passed = false;
+    }
+
+    // ── pnpm (if frontend/ directory exists) ─────────────────────
+    let frontend_dir = project_root.join("frontend");
+    if frontend_dir.exists() {
+        all_output.push_str("=== pnpm build ===\n");
+        let pnpm_build = Command::new("pnpm")
+            .args(["run", "build"])
+            .current_dir(&frontend_dir)
+            .output()
+            .map_err(|e| format!("Failed to run pnpm build: {e}"))?;
+
+        let build_out = format!(
+            "{}{}",
+            String::from_utf8_lossy(&pnpm_build.stdout),
+            String::from_utf8_lossy(&pnpm_build.stderr)
+        );
+        all_output.push_str(&build_out);
+        all_output.push('\n');
+
+        if !pnpm_build.status.success() {
+            all_passed = false;
+        }
+
+        all_output.push_str("=== pnpm test ===\n");
+        let pnpm_test = Command::new("pnpm")
+            .args(["test", "--run"])
+            .current_dir(&frontend_dir)
+            .output()
+            .map_err(|e| format!("Failed to run pnpm test: {e}"))?;
+
+        let test_out = format!(
+            "{}{}",
+            String::from_utf8_lossy(&pnpm_test.stdout),
+            String::from_utf8_lossy(&pnpm_test.stderr)
+        );
+        all_output.push_str(&test_out);
+        all_output.push('\n');
+
+        if !pnpm_test.status.success() {
+            all_passed = false;
+        }
+    }
+
+    Ok((all_passed, all_output))
+}
+
 /// Spawn claude agent in a PTY and stream events through the broadcast channel.
 #[allow(clippy::too_many_arguments)]
 async fn run_agent_pty_streaming(
@@ -1504,4 +1831,210 @@ mod tests {
         let log = String::from_utf8_lossy(&output.stdout);
         assert!(log.contains("story-kit: test commit"), "commit should appear in log: {log}");
     }
+
+    // ── move_story_to_merge tests ──────────────────────────────────────────────
+
+    #[test]
+    fn move_story_to_merge_moves_file_and_commits() {
+        use std::fs;
+        use tempfile::tempdir;
+
+        let tmp = tempdir().unwrap();
+        let repo = tmp.path();
+        init_git_repo(repo);
+
+        let current_dir = repo.join(".story_kit/work/2_current");
+        fs::create_dir_all(&current_dir).unwrap();
+        let story_file = current_dir.join("20_story_my_story.md");
+        fs::write(&story_file, "---\nname: Test\ntest_plan: approved\n---\n").unwrap();
+
+        Command::new("git")
+            .args(["add", "."])
+            .current_dir(repo)
+            .output()
+            .unwrap();
+        Command::new("git")
+            .args(["commit", "-m", "add story"])
+            .current_dir(repo)
+            .output()
+            .unwrap();
+
+        move_story_to_merge(repo, "20_story_my_story").unwrap();
+
+        let merge_path = repo.join(".story_kit/work/4_merge/20_story_my_story.md");
+        assert!(!story_file.exists(), "2_current file should be gone");
+        assert!(merge_path.exists(), "4_merge file should exist");
+    }
+
+    #[test]
+    fn move_story_to_merge_idempotent_when_already_in_merge() {
+        use std::fs;
+        use tempfile::tempdir;
+
+        let tmp = tempdir().unwrap();
+        let repo = tmp.path();
+        init_git_repo(repo);
+
+        let merge_dir = repo.join(".story_kit/work/4_merge");
+        fs::create_dir_all(&merge_dir).unwrap();
+        fs::write(
+            merge_dir.join("21_story_test.md"),
+            "---\nname: Test\ntest_plan: approved\n---\n",
+        )
+        .unwrap();
+
+        // Should succeed without error even though there's nothing to move
+        move_story_to_merge(repo, "21_story_test").unwrap();
+        assert!(merge_dir.join("21_story_test.md").exists());
+    }
+
+    #[test]
+    fn move_story_to_merge_errors_when_not_in_current() {
+        use tempfile::tempdir;
+
+        let tmp = tempdir().unwrap();
+        let repo = tmp.path();
+        init_git_repo(repo);
+
+        let result = move_story_to_merge(repo, "99_nonexistent");
+        assert!(result.is_err());
+        assert!(result.unwrap_err().contains("not found in work/2_current/"));
+    }
+
+    // ── move_story_to_archived with 4_merge source ────────────────────────────
+
+    #[test]
+    fn move_story_to_archived_finds_in_merge_dir() {
+        use std::fs;
+        use tempfile::tempdir;
+
+        let tmp = tempdir().unwrap();
+        let repo = tmp.path();
+        init_git_repo(repo);
+
+        let merge_dir = repo.join(".story_kit/work/4_merge");
+        fs::create_dir_all(&merge_dir).unwrap();
+        let story_file = merge_dir.join("22_story_test.md");
+        fs::write(&story_file, "---\nname: Test\ntest_plan: approved\n---\n").unwrap();
+
+        Command::new("git")
+            .args(["add", "."])
+            .current_dir(repo)
+            .output()
+            .unwrap();
+        Command::new("git")
+            .args(["commit", "-m", "add story in merge"])
+            .current_dir(repo)
+            .output()
+            .unwrap();
+
+        move_story_to_archived(repo, "22_story_test").unwrap();
+
+        let archived = repo.join(".story_kit/work/5_archived/22_story_test.md");
+        assert!(!story_file.exists(), "4_merge file should be gone");
+        assert!(archived.exists(), "5_archived file should exist");
+    }
+
+    #[test]
+    fn move_story_to_archived_error_when_not_in_current_or_merge() {
+        use tempfile::tempdir;
+
+        let tmp = tempdir().unwrap();
+        let repo = tmp.path();
+        init_git_repo(repo);
+
+        let result = move_story_to_archived(repo, "99_nonexistent");
+        assert!(result.is_err());
+        let msg = result.unwrap_err();
+        assert!(msg.contains("4_merge"), "error should mention 4_merge: {msg}");
+    }
+
+    // ── merge_agent_work tests ────────────────────────────────────────────────
+
+    #[tokio::test]
+    async fn merge_agent_work_returns_error_when_branch_not_found() {
+        use tempfile::tempdir;
+
+        let tmp = tempdir().unwrap();
+        let repo = tmp.path();
+        init_git_repo(repo);
+
+        let pool = AgentPool::new(3001);
+        // branch feature/story-99_nonexistent does not exist
+        let result = pool
+            .merge_agent_work(repo, "99_nonexistent")
+            .await
+            .unwrap();
+        // Should fail (no branch) — not panic
+        assert!(!result.success, "should fail when branch missing");
+    }
+
+    #[tokio::test]
+    async fn merge_agent_work_succeeds_on_clean_branch() {
+        use std::fs;
+        use tempfile::tempdir;
+
+        let tmp = tempdir().unwrap();
+        let repo = tmp.path();
+        init_git_repo(repo);
+
+        // Create a feature branch with a commit
+        Command::new("git")
+            .args(["checkout", "-b", "feature/story-23_test"])
+            .current_dir(repo)
+            .output()
+            .unwrap();
+        fs::write(repo.join("feature.txt"), "feature content").unwrap();
+        Command::new("git")
+            .args(["add", "."])
+            .current_dir(repo)
+            .output()
+            .unwrap();
+        Command::new("git")
+            .args(["commit", "-m", "add feature"])
+            .current_dir(repo)
+            .output()
+            .unwrap();
+
+        // Switch back to master (initial branch)
+        Command::new("git")
+            .args(["checkout", "master"])
+            .current_dir(repo)
+            .output()
+            .unwrap();
+
+        // Create the story file in 4_merge/ so we can test archival
+        let merge_dir = repo.join(".story_kit/work/4_merge");
+        fs::create_dir_all(&merge_dir).unwrap();
+        let story_file = merge_dir.join("23_test.md");
+        fs::write(&story_file, "---\nname: Test\ntest_plan: approved\n---\n").unwrap();
+        Command::new("git")
+            .args(["add", "."])
+            .current_dir(repo)
+            .output()
+            .unwrap();
+        Command::new("git")
+            .args(["commit", "-m", "add story in merge"])
+            .current_dir(repo)
+            .output()
+            .unwrap();
+
+        let pool = AgentPool::new(3001);
+        let report = pool.merge_agent_work(repo, "23_test").await.unwrap();
+
+        // Merge should succeed (gates will run but cargo/pnpm results will depend on env)
+        // At minimum the merge itself should succeed
+        assert!(!report.had_conflicts, "should have no conflicts");
+        // Note: gates_passed may be false in test env without Rust project, that's OK
+        // The important thing is the merge itself ran
+        assert!(
+            report.success || report.gate_output.contains("Failed to run") || !report.gates_passed,
+            "report should be coherent: {report:?}"
+        );
+        // Story should be archived if gates passed
+        if report.story_archived {
+            let archived = repo.join(".story_kit/work/5_archived/23_test.md");
+            assert!(archived.exists(), "archived file should exist");
+        }
+    }
 }
diff --git a/server/src/http/mcp.rs b/server/src/http/mcp.rs
index 91c4a81..b2eb469 100644
--- a/server/src/http/mcp.rs
+++ b/server/src/http/mcp.rs
@@ -1,4 +1,4 @@
-use crate::agents::move_story_to_archived;
+use crate::agents::{close_bug_to_archive, move_story_to_archived, move_story_to_merge};
 use crate::config::ProjectConfig;
 use crate::http::context::AppContext;
 use crate::http::settings::get_editor_command_from_store;
@@ -6,7 +6,6 @@ use crate::http::workflow::{
     check_criterion_in_file, create_bug_file, create_story_file, list_bug_files,
     load_upcoming_stories, set_test_plan_in_file, validate_story_dirs,
 };
-use crate::agents::close_bug_to_archive;
 use crate::worktree;
 use crate::io::story_metadata::{parse_front_matter, parse_unchecked_todos};
 use crate::workflow::{evaluate_acceptance_with_coverage, TestCaseResult, TestStatus};
@@ -711,6 +710,38 @@ fn handle_tools_list(id: Option<Value>) -> JsonRpcResponse {
                         },
                         "required": ["bug_id"]
                     }
+                },
+                {
+                    "name": "merge_agent_work",
+                    "description": "Trigger the mergemaster pipeline for a completed story: squash-merge the feature branch into master, run quality gates (cargo clippy, cargo test, pnpm build, pnpm test), archive the story from work/4_merge/ or work/2_current/ to work/5_archived/, and clean up the worktree and branch. Reports success/failure with details including any conflicts found and gate output.",
+                    "inputSchema": {
+                        "type": "object",
+                        "properties": {
+                            "story_id": {
+                                "type": "string",
+                                "description": "Story identifier (e.g. '52_story_mergemaster_agent_role')"
+                            },
+                            "agent_name": {
+                                "type": "string",
+                                "description": "Optional: name of the coder agent whose work is being merged (for logging)"
+                            }
+                        },
+                        "required": ["story_id"]
+                    }
+                },
+                {
+                    "name": "move_story_to_merge",
+                    "description": "Move a story or bug from work/2_current/ to work/4_merge/ to queue it for the mergemaster pipeline. Auto-commits to master.",
+                    "inputSchema": {
+                        "type": "object",
+                        "properties": {
+                            "story_id": {
+                                "type": "string",
+                                "description": "Story identifier (filename stem, e.g. '28_my_story')"
+                            }
+                        },
+                        "required": ["story_id"]
+                    }
                 }
             ]
         }),
@@ -763,6 +794,9 @@ async fn handle_tools_call(
         "create_bug" => tool_create_bug(&args, ctx),
         "list_bugs" => tool_list_bugs(ctx),
         "close_bug" => tool_close_bug(&args, ctx),
+        // Mergemaster tools
+        "merge_agent_work" => tool_merge_agent_work(&args, ctx).await,
+        "move_story_to_merge" => tool_move_story_to_merge(&args, ctx),
         _ => Err(format!("Unknown tool: {tool_name}")),
     };
 
@@ -1275,6 +1309,57 @@ fn tool_close_bug(args: &Value, ctx: &AppContext) -> Result<String, String> {
     ))
 }
 
+// ── Mergemaster tool implementations ─────────────────────────────
+
+async fn tool_merge_agent_work(args: &Value, ctx: &AppContext) -> Result<String, String> {
+    let story_id = args
+        .get("story_id")
+        .and_then(|v| v.as_str())
+        .ok_or("Missing required argument: story_id")?;
+    let agent_name = args.get("agent_name").and_then(|v| v.as_str());
+
+    let project_root = ctx.agents.get_project_root(&ctx.state)?;
+    let report = ctx.agents.merge_agent_work(&project_root, story_id).await?;
+
+    let status_msg = if report.success && report.gates_passed {
+        "Merge complete: all quality gates passed. Story archived and worktree cleaned up."
+    } else if report.had_conflicts {
+        "Merge failed: conflicts detected. Merge was aborted. Resolve conflicts manually and retry."
+    } else if report.success && !report.gates_passed {
+        "Merge committed but quality gates failed. Review gate_output and fix issues before re-running."
+    } else {
+        "Merge failed. Review gate_output for details."
+    };
+
+    serde_json::to_string_pretty(&json!({
+        "story_id": story_id,
+        "agent_name": agent_name,
+        "success": report.success,
+        "had_conflicts": report.had_conflicts,
+        "conflict_details": report.conflict_details,
+        "gates_passed": report.gates_passed,
+        "gate_output": report.gate_output,
+        "worktree_cleaned_up": report.worktree_cleaned_up,
+        "story_archived": report.story_archived,
+        "message": status_msg,
+    }))
+    .map_err(|e| format!("Serialization error: {e}"))
+}
+
+fn tool_move_story_to_merge(args: &Value, ctx: &AppContext) -> Result<String, String> {
+    let story_id = args
+        .get("story_id")
+        .and_then(|v| v.as_str())
+        .ok_or("Missing required argument: story_id")?;
+
+    let project_root = ctx.agents.get_project_root(&ctx.state)?;
+    move_story_to_merge(&project_root, story_id)?;
+
+    Ok(format!(
+        "Story '{story_id}' moved to work/4_merge/ and committed. Ready for mergemaster."
+    ))
+}
+
 /// Run `git log <base>..HEAD --oneline` in the worktree and return the commit
 /// summaries, or `None` if git is unavailable or there are no new commits.
 async fn get_worktree_commits(worktree_path: &str, base_branch: &str) -> Option<Vec<String>> {
@@ -1432,7 +1517,9 @@ mod tests {
         assert!(names.contains(&"create_bug"));
         assert!(names.contains(&"list_bugs"));
         assert!(names.contains(&"close_bug"));
-        assert_eq!(tools.len(), 24);
+        assert!(names.contains(&"merge_agent_work"));
+        assert!(names.contains(&"move_story_to_merge"));
+        assert_eq!(tools.len(), 26);
     }
 
     #[test]
@@ -2021,4 +2108,104 @@ mod tests {
         assert!(!bug_file.exists());
         assert!(tmp.path().join(".story_kit/work/5_archived/1_bug_crash.md").exists());
     }
+
+    // ── Mergemaster tool tests ─────────────────────────────────────────────
+
+    #[test]
+    fn merge_agent_work_in_tools_list() {
+        let resp = handle_tools_list(Some(json!(1)));
+        let tools = resp.result.unwrap()["tools"].as_array().unwrap().clone();
+        let tool = tools.iter().find(|t| t["name"] == "merge_agent_work");
+        assert!(tool.is_some(), "merge_agent_work missing from tools list");
+        let t = tool.unwrap();
+        assert!(t["description"].is_string());
+        let required = t["inputSchema"]["required"].as_array().unwrap();
+        let req_names: Vec<&str> = required.iter().map(|v| v.as_str().unwrap()).collect();
+        assert!(req_names.contains(&"story_id"));
+        // agent_name is optional
+        assert!(!req_names.contains(&"agent_name"));
+    }
+
+    #[test]
+    fn move_story_to_merge_in_tools_list() {
+        let resp = handle_tools_list(Some(json!(1)));
+        let tools = resp.result.unwrap()["tools"].as_array().unwrap().clone();
+        let tool = tools.iter().find(|t| t["name"] == "move_story_to_merge");
+        assert!(tool.is_some(), "move_story_to_merge missing from tools list");
+        let t = tool.unwrap();
+        assert!(t["description"].is_string());
+        let required = t["inputSchema"]["required"].as_array().unwrap();
+        let req_names: Vec<&str> = required.iter().map(|v| v.as_str().unwrap()).collect();
+        assert!(req_names.contains(&"story_id"));
+    }
+
+    #[tokio::test]
+    async fn tool_merge_agent_work_missing_story_id() {
+        let tmp = tempfile::tempdir().unwrap();
+        let ctx = test_ctx(tmp.path());
+        let result = tool_merge_agent_work(&json!({}), &ctx).await;
+        assert!(result.is_err());
+        assert!(result.unwrap_err().contains("story_id"));
+    }
+
+    #[test]
+    fn tool_move_story_to_merge_missing_story_id() {
+        let tmp = tempfile::tempdir().unwrap();
+        let ctx = test_ctx(tmp.path());
+        let result = tool_move_story_to_merge(&json!({}), &ctx);
+        assert!(result.is_err());
+        assert!(result.unwrap_err().contains("story_id"));
+    }
+
+    #[test]
+    fn tool_move_story_to_merge_moves_file() {
+        let tmp = tempfile::tempdir().unwrap();
+        setup_git_repo_in(tmp.path());
+        let current_dir = tmp.path().join(".story_kit/work/2_current");
+        std::fs::create_dir_all(&current_dir).unwrap();
+        let story_file = current_dir.join("24_story_test.md");
+        std::fs::write(&story_file, "---\nname: Test\ntest_plan: approved\n---\n").unwrap();
+        std::process::Command::new("git")
+            .args(["add", "."])
+            .current_dir(tmp.path())
+            .output()
+            .unwrap();
+        std::process::Command::new("git")
+            .args(["commit", "-m", "add story"])
+            .current_dir(tmp.path())
+            .output()
+            .unwrap();
+
+        let ctx = test_ctx(tmp.path());
+        let result = tool_move_story_to_merge(&json!({"story_id": "24_story_test"}), &ctx).unwrap();
+        assert!(result.contains("4_merge"));
+        assert!(!story_file.exists(), "2_current file should be gone");
+        assert!(
+            tmp.path().join(".story_kit/work/4_merge/24_story_test.md").exists(),
+            "4_merge file should exist"
+        );
+    }
+
+    #[tokio::test]
+    async fn tool_merge_agent_work_returns_coherent_report() {
+        let tmp = tempfile::tempdir().unwrap();
+        setup_git_repo_in(tmp.path());
+        let ctx = test_ctx(tmp.path());
+
+        // Try to merge a non-existent branch — should return a report (not panic)
+        let result = tool_merge_agent_work(
+            &json!({"story_id": "99_nonexistent", "agent_name": "coder-1"}),
+            &ctx,
+        )
+        .await
+        .unwrap();
+        let parsed: Value = serde_json::from_str(&result).unwrap();
+        assert_eq!(parsed["story_id"], "99_nonexistent");
+        assert_eq!(parsed["agent_name"], "coder-1");
+        assert!(parsed.get("success").is_some());
+        assert!(parsed.get("had_conflicts").is_some());
+        assert!(parsed.get("gates_passed").is_some());
+        assert!(parsed.get("gate_output").is_some());
+        assert!(parsed.get("message").is_some());
+    }
 }