Supports switching default board

src/commands/board.rs

@@ -80,6 +80,15 @@ pub fn list_boards(project_dir: Option<&str>) -> Result<()> {
         "anvil board --add mega".bright_cyan()
     );
     if config.boards.len() > 1 {
+        println!(
+            "  Set default:    {}",
+            format!(
+                "anvil board --default {}",
+                config.boards.keys()
+                    .find(|k| *k != &config.build.default)
+                    .unwrap_or(&config.build.default)
+            ).bright_cyan()
+        );
         println!(
             "  Remove a board: {}",
             format!(
@@ -446,7 +455,7 @@ pub fn remove_board(name: &str, project_dir: Option<&str>) -> Result<()> {
     if name == config.build.default {
         bail!(
             "Cannot remove '{}' because it is the default board.\n  \
-             Change the default in .anvil.toml first, or remove a different board.",
+             Change the default first: anvil board --default <other-board>",
             name
         );
     }
@@ -495,6 +504,53 @@ pub fn remove_board(name: &str, project_dir: Option<&str>) -> Result<()> {
     Ok(())
 }
 
+/// Set the default board in .anvil.toml.
+pub fn set_default_board(name: &str, project_dir: Option<&str>) -> Result<()> {
+    let project_path = resolve_project_dir(project_dir)?;
+    let config = ProjectConfig::load(&project_path)?;
+
+    // Verify the board exists
+    if !config.boards.contains_key(name) {
+        let available: Vec<&String> = config.boards.keys().collect();
+        if available.is_empty() {
+            bail!(
+                "No board '{}' found.\n  \
+                 Add it first: anvil board --add {}",
+                name, name
+            );
+        } else {
+            bail!(
+                "No board '{}' found.\n  \
+                 Available: {}\n  \
+                 Add it first: anvil board --add {}",
+                name,
+                available.iter().map(|s| s.as_str()).collect::<Vec<_>>().join(", "),
+                name
+            );
+        }
+    }
+
+    let config_path = project_path.join(CONFIG_FILENAME);
+    let old = crate::project::config::set_default_in_file(&config_path, name)?;
+
+    let label = board_label(&config.boards[name].fqbn);
+    println!(
+        "{} Default board: {} ({})",
+        "ok".green(),
+        name.bright_white().bold(),
+        label.bright_cyan()
+    );
+    if !old.is_empty() && old != name {
+        println!(
+            "  {}",
+            format!("Changed from: {}", old).bright_black()
+        );
+    }
+    println!();
+
+    Ok(())
+}
+
 fn resolve_project_dir(project_dir: Option<&str>) -> Result<std::path::PathBuf> {
     let start = match project_dir {
         Some(dir) => std::path::PathBuf::from(dir),