feat(commands): slash-command validation, help formatting, CLI wiring

- Add centralized validate_slash_command_input for all slash commands
- Rich error messages and per-command help detail
- Wire validation into CLI entrypoints in main.rs
- Consistent /agents and /skills usage surface
- Verified: cargo test -p commands 22 passed, integration test passed, clippy clean

rust/crates/rusty-claude-cli/src/main.rs

@@ -22,7 +22,8 @@ use api::{
 
 use commands::{
     handle_agents_slash_command, handle_plugins_slash_command, handle_skills_slash_command,
-    render_slash_command_help, resume_supported_slash_commands, slash_command_specs, SlashCommand,
+    render_slash_command_help, resume_supported_slash_commands, slash_command_specs,
+    validate_slash_command_input, SlashCommand,
 };
 use compat_harness::{extract_manifest, UpstreamPaths};
 use init::initialize_repo;
@@ -422,12 +423,12 @@ fn join_optional_args(args: &[String]) -> Option<String> {
 
 fn parse_direct_slash_cli_action(rest: &[String]) -> Result<CliAction, String> {
     let raw = rest.join(" ");
-    match SlashCommand::parse(&raw) {
-        Some(SlashCommand::Help) => Ok(CliAction::Help),
-        Some(SlashCommand::Agents { args }) => Ok(CliAction::Agents { args }),
-        Some(SlashCommand::Skills { args }) => Ok(CliAction::Skills { args }),
-        Some(SlashCommand::Unknown(name)) => Err(format_unknown_direct_slash_command(&name)),
-        Some(command) => Err({
+    match validate_slash_command_input(&raw) {
+        Ok(Some(SlashCommand::Help)) => Ok(CliAction::Help),
+        Ok(Some(SlashCommand::Agents { args })) => Ok(CliAction::Agents { args }),
+        Ok(Some(SlashCommand::Skills { args })) => Ok(CliAction::Skills { args }),
+        Ok(Some(SlashCommand::Unknown(name))) => Err(format_unknown_direct_slash_command(&name)),
+        Ok(Some(command)) => Err({
             let _ = command;
             format!(
                 "slash command {command_name} is interactive-only. Start `claw` and run it there, or use `claw --resume SESSION.jsonl {command_name}` / `claw --resume {latest} {command_name}` when the command is marked [resume] in /help.",
@@ -435,7 +436,8 @@ fn parse_direct_slash_cli_action(rest: &[String]) -> Result<CliAction, String> {
                 latest = LATEST_SESSION_REFERENCE,
             )
         }),
-        None => Err(format!("unknown subcommand: {}", rest[0])),
+        Ok(None) => Err(format!("unknown subcommand: {}", rest[0])),
+        Err(error) => Err(error.to_string()),
     }
 }
 
@@ -896,9 +898,16 @@ fn resume_session(session_path: &Path, commands: &[String]) {
 
     let mut session = session;
     for raw_command in commands {
-        let Some(command) = SlashCommand::parse(raw_command) else {
-            eprintln!("unsupported resumed command: {raw_command}");
-            std::process::exit(2);
+        let command = match validate_slash_command_input(raw_command) {
+            Ok(Some(command)) => command,
+            Ok(None) => {
+                eprintln!("unsupported resumed command: {raw_command}");
+                std::process::exit(2);
+            }
+            Err(error) => {
+                eprintln!("{error}");
+                std::process::exit(2);
+            }
         };
         match run_resume_command(&resolved_path, &session, &command) {
             Ok(ResumeCommandOutcome {
@@ -1417,11 +1426,18 @@ fn run_repl(
                     cli.persist_session()?;
                     break;
                 }
-                if let Some(command) = SlashCommand::parse(&trimmed) {
-                    if cli.handle_repl_command(command)? {
-                        cli.persist_session()?;
+                match validate_slash_command_input(&trimmed) {
+                    Ok(Some(command)) => {
+                        if cli.handle_repl_command(command)? {
+                            cli.persist_session()?;
+                        }
+                        continue;
+                    }
+                    Ok(None) => {}
+                    Err(error) => {
+                        eprintln!("{error}");
+                        continue;
                     }
-                    continue;
                 }
                 editor.push_history(input);
                 cli.run_turn(&trimmed)?;
@@ -5246,6 +5262,23 @@ mod tests {
         assert!(error.contains("claw --resume SESSION.jsonl /status"));
     }
 
+    #[test]
+    fn direct_slash_commands_surface_shared_validation_errors() {
+        let compact_error = parse_args(&["/compact".to_string(), "now".to_string()])
+            .expect_err("invalid /compact shape should be rejected");
+        assert!(compact_error.contains("Unexpected arguments for /compact."));
+        assert!(compact_error.contains("Usage            /compact"));
+
+        let plugins_error = parse_args(&[
+            "/plugins".to_string(),
+            "list".to_string(),
+            "extra".to_string(),
+        ])
+        .expect_err("invalid /plugins list shape should be rejected");
+        assert!(plugins_error.contains("Usage: /plugin list"));
+        assert!(plugins_error.contains("Aliases          /plugins, /marketplace"));
+    }
+
     #[test]
     fn formats_unknown_slash_command_with_suggestions() {
         let report = format_unknown_slash_command_message("stats");