story-209: accept optional positional path argument on startup

Add CLI path argument support: `story-kit-server /path/to/project` opens
the given project directly (scaffolding .story_kit/ if needed) instead of
relying on auto-detection. Resolves conflict with story-208's port parameter.

Squash merge of feature/story-209

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

server/src/io/fs.rs

@@ -383,6 +383,19 @@ To support both Remote and Local models, the system implements a `ModelProvider`
 
 const STORY_KIT_SCRIPT_TEST: &str = "#!/usr/bin/env bash\nset -euo pipefail\n\n# Add your project's test commands here.\n# Story Kit agents invoke this script as the canonical test runner.\n# Exit 0 on success, non-zero on failure.\necho \"No tests configured\"\n";
 
+/// Resolve a path argument supplied on the CLI against the given working
+/// directory.  Relative paths (including `.`) are joined with `cwd` and
+/// then canonicalized when possible.  Absolute paths are returned
+/// canonicalized when possible, unchanged otherwise.
+pub fn resolve_cli_path(cwd: &Path, path_arg: &str) -> PathBuf {
+    let p = PathBuf::from(path_arg);
+    let joined = if p.is_absolute() { p } else { cwd.join(p) };
+    // Canonicalize resolves `.`, `..` and symlinks.  We fall back to the
+    // joined (non-canonical) path when the target does not yet exist so
+    // that callers can still create it later.
+    std::fs::canonicalize(&joined).unwrap_or(joined)
+}
+
 /// Walk from `start` up through parent directories, returning the first
 /// directory that contains a `.story_kit/` subdirectory, or `None`.
 pub fn find_story_kit_root(start: &Path) -> Option<PathBuf> {
@@ -493,6 +506,8 @@ async fn ensure_project_root_with_story_kit(path: PathBuf) -> Result<(), String>
         if !path.exists() {
             fs::create_dir_all(&path)
                 .map_err(|e| format!("Failed to create project directory: {}", e))?;
+        }
+        if !path.join(".story_kit").is_dir() {
             scaffold_story_kit(&path)?;
         }
         Ok(())
@@ -1058,4 +1073,86 @@ mod tests {
 
         assert_eq!(fs::read_to_string(&readme).unwrap(), "custom content");
     }
+
+    // --- open_project scaffolding ---
+
+    #[tokio::test]
+    async fn open_project_scaffolds_when_story_kit_missing() {
+        let dir = tempdir().unwrap();
+        let project_dir = dir.path().join("myproject");
+        fs::create_dir_all(&project_dir).unwrap();
+        let store = make_store(&dir);
+        let state = SessionState::default();
+
+        open_project(
+            project_dir.to_string_lossy().to_string(),
+            &state,
+            &store,
+        )
+        .await
+        .unwrap();
+
+        // .story_kit/ should have been created automatically
+        assert!(project_dir.join(".story_kit").is_dir());
+    }
+
+    #[tokio::test]
+    async fn open_project_does_not_overwrite_existing_story_kit() {
+        let dir = tempdir().unwrap();
+        let project_dir = dir.path().join("myproject");
+        let sk_dir = project_dir.join(".story_kit");
+        fs::create_dir_all(&sk_dir).unwrap();
+        let readme = sk_dir.join("README.md");
+        fs::write(&readme, "custom content").unwrap();
+        let store = make_store(&dir);
+        let state = SessionState::default();
+
+        open_project(
+            project_dir.to_string_lossy().to_string(),
+            &state,
+            &store,
+        )
+        .await
+        .unwrap();
+
+        // Existing .story_kit/ content should not be overwritten
+        assert_eq!(fs::read_to_string(&readme).unwrap(), "custom content");
+    }
+
+    // --- resolve_cli_path ---
+
+    #[test]
+    fn resolve_cli_path_absolute_returned_unchanged_when_nonexistent() {
+        let cwd = PathBuf::from("/some/cwd");
+        let result = resolve_cli_path(&cwd, "/nonexistent/absolute/path");
+        assert_eq!(result, PathBuf::from("/nonexistent/absolute/path"));
+    }
+
+    #[test]
+    fn resolve_cli_path_dot_resolves_to_cwd() {
+        let tmp = tempdir().unwrap();
+        let cwd = tmp.path().to_path_buf();
+        let result = resolve_cli_path(&cwd, ".");
+        // Canonicalize should resolve "." in an existing dir to the canonical cwd
+        assert_eq!(result, cwd.canonicalize().unwrap_or(cwd));
+    }
+
+    #[test]
+    fn resolve_cli_path_relative_resolves_against_cwd() {
+        let tmp = tempdir().unwrap();
+        let cwd = tmp.path().to_path_buf();
+        let subdir = cwd.join("sub");
+        fs::create_dir_all(&subdir).unwrap();
+        let result = resolve_cli_path(&cwd, "sub");
+        assert_eq!(result, subdir.canonicalize().unwrap_or(subdir));
+    }
+
+    #[test]
+    fn resolve_cli_path_nonexistent_relative_falls_back_to_joined() {
+        let tmp = tempdir().unwrap();
+        let cwd = tmp.path().to_path_buf();
+        let result = resolve_cli_path(&cwd, "newproject");
+        // Path doesn't exist yet — canonicalize fails, fallback is cwd/newproject
+        assert_eq!(result, cwd.join("newproject"));
+    }
 }