Accept story 45: Deterministic Story Lifecycle Management

- accept_story MCP tool moves current/ to archived/
- move_story_to_archived helper with idempotent behavior
- start_agent auto-moves upcoming/ to current/

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

server/src/http/mcp.rs

@@ -1,3 +1,4 @@
+use crate::agents::move_story_to_archived;
 use crate::config::ProjectConfig;
 use crate::http::context::AppContext;
 use crate::http::settings::get_editor_command_from_store;
@@ -599,6 +600,20 @@ fn handle_tools_list(id: Option<Value>) -> JsonRpcResponse {
                         },
                         "required": ["story_id", "agent_name", "summary"]
                     }
+                },
+                {
+                    "name": "accept_story",
+                    "description": "Accept a story: moves it from current/ to archived/.",
+                    "inputSchema": {
+                        "type": "object",
+                        "properties": {
+                            "story_id": {
+                                "type": "string",
+                                "description": "Story identifier (filename stem, e.g. '28_my_story')"
+                            }
+                        },
+                        "required": ["story_id"]
+                    }
                 }
             ]
         }),
@@ -642,6 +657,8 @@ async fn handle_tools_call(
         "get_editor_command" => tool_get_editor_command(&args, ctx),
         // Completion reporting
         "report_completion" => tool_report_completion(&args, ctx).await,
+        // Lifecycle tools
+        "accept_story" => tool_accept_story(&args, ctx),
         _ => Err(format!("Unknown tool: {tool_name}")),
     };
 
@@ -1041,6 +1058,18 @@ async fn tool_report_completion(args: &Value, ctx: &AppContext) -> Result<String
     .map_err(|e| format!("Serialization error: {e}"))
 }
 
+fn tool_accept_story(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_archived(&project_root, story_id)?;
+
+    Ok(format!("Story '{story_id}' accepted and moved to archived/."))
+}
+
 /// 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>> {
@@ -1192,7 +1221,8 @@ mod tests {
         assert!(names.contains(&"remove_worktree"));
         assert!(names.contains(&"get_editor_command"));
         assert!(names.contains(&"report_completion"));
-        assert_eq!(tools.len(), 18);
+        assert!(names.contains(&"accept_story"));
+        assert_eq!(tools.len(), 19);
     }
 
     #[test]