Clarify allowed tool status handling

Reject empty --allowedTools inputs instead of treating them as an empty restriction, and surface status JSON metadata that distinguishes default unrestricted tools from flag-provided allow lists.

Confidence: high
Scope-risk: narrow
Tested: cargo test -p rusty-claude-cli rejects_empty_allowed_tools_flag -- --nocapture
Tested: cargo test -p tools allowed_tools_rejects_empty_token_lists -- --nocapture
Tested: cargo check -p rusty-claude-cli -p tools
Tested: cargo test -p rusty-claude-cli -p tools
Not-tested: full workspace cargo fmt --check is blocked by pre-existing unrelated formatting drift

rust/crates/tools/src/lib.rs

@@ -240,6 +240,13 @@ impl GlobalToolRegistry {
             }
         }
 
+        if allowed.is_empty() {
+            return Err(format!(
+                "--allowedTools was provided with no usable tool names (got `{}`). Omit the flag to allow all tools.",
+                values.join(" ")
+            ));
+        }
+
         Ok(Some(allowed))
     }
 
@@ -6883,6 +6890,21 @@ mod tests {
         assert!(empty_permission.contains("unsupported plugin permission: "));
     }
 
+    #[test]
+    fn allowed_tools_rejects_empty_token_lists() {
+        let registry = GlobalToolRegistry::builtin();
+
+        for raw in ["", ",,", "   "] {
+            let err = registry
+                .normalize_allowed_tools(&[raw.to_string()])
+                .expect_err("empty allow-list input should be rejected");
+            assert!(
+                err.contains("--allowedTools was provided with no usable tool names"),
+                "unexpected error for {raw:?}: {err}"
+            );
+        }
+    }
+
     #[test]
     fn runtime_tools_extend_registry_definitions_permissions_and_search() {
         let registry = GlobalToolRegistry::builtin()