fix(#768): --resume non-slash trailing arg now has error_kind:invalid_resume_argument + hint

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

@@ -331,6 +331,9 @@ fn classify_error_kind(message: &str) -> &'static str {
     } else if message.starts_with("unexpected extra arguments") {
         // #766: extra positionals after commands that take no arguments (e.g. claw diff)
         "unexpected_extra_args"
+    } else if message.starts_with("invalid_resume_argument:") {
+        // #768: --resume trailing arg is not a slash command
+        "invalid_resume_argument"
     } else if message.starts_with("unknown_option:") {
         "unknown_option"
     } else if message.contains("is a slash command")
@@ -2102,7 +2105,10 @@ fn parse_resume_args(args: &[String], output_format: CliOutputFormat) -> Result<
         }
 
         if current_command.is_empty() {
-            return Err("--resume trailing arguments must be slash commands".to_string());
+            // #768: typed prefix + \n hint so split_error_hint() extracts hint into JSON envelope
+            return Err(format!(
+                "invalid_resume_argument: `{token}` is not a slash command.\nUsage: claw --resume <session-id|latest> /<slash-command>  (e.g. /compact, /status)"
+            ));
         }
 
         current_command.push(' ');
@@ -12957,6 +12963,13 @@ mod tests {
             ),
             "removed_subcommand"
         );
+        // #768: invalid resume trailing arg must classify as invalid_resume_argument
+        assert_eq!(
+            classify_error_kind(
+                "invalid_resume_argument: `compact` is not a slash command.\nUsage: claw --resume <session-id|latest> /<slash-command>"
+            ),
+            "invalid_resume_argument"
+        );
     }
 
     #[test]

rust/crates/rusty-claude-cli/tests/output_format_contract.rs

@@ -1940,3 +1940,43 @@ fn diff_extra_args_have_typed_error_kind_and_hint_766() {
         "claw diff --bogus must return non-null hint (#766), got: {hint:?}"
     );
 }
+
+#[test]
+fn resume_non_slash_trailing_arg_has_typed_error_kind_and_hint_768() {
+    // #768: `claw --resume latest compact` (missing leading /) returned
+    // error_kind:"unknown" + hint:null. Resume is orchestration-critical;
+    // wrappers need a machine-readable signal with a recovery hint.
+    let root = unique_temp_dir("resume-invalid-arg-768");
+    fs::create_dir_all(&root).expect("temp dir should exist");
+
+    let output = run_claw(
+        &root,
+        &["--output-format", "json", "--resume", "latest", "compact"],
+        &[],
+    );
+    assert!(
+        !output.status.success(),
+        "claw --resume latest compact should exit non-zero"
+    );
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    let json_line = stderr
+        .lines()
+        .find(|l| l.trim_start().starts_with('{'))
+        .expect("stderr should contain a JSON error envelope");
+    let parsed: serde_json::Value =
+        serde_json::from_str(json_line).expect("error envelope should be valid JSON");
+
+    assert_eq!(
+        parsed["error_kind"], "invalid_resume_argument",
+        "non-slash resume trailing arg must return error_kind:invalid_resume_argument (#768)"
+    );
+    let hint = parsed["hint"].as_str().unwrap_or("");
+    assert!(
+        !hint.is_empty(),
+        "non-slash resume trailing arg must return non-null hint (#768), got: {hint:?}"
+    );
+    assert!(
+        hint.contains("/compact") || hint.contains("slash-command"),
+        "hint must reference slash-command usage, got: {hint:?}"
+    );
+}