fix(channels): enforce reply_target naming consistency

tests/reply_target_field_regression.rs

@@ -0,0 +1,70 @@
+//! Regression guard for ChannelMessage field naming consistency.
+//!
+//! This test prevents accidental reintroduction of the removed `reply_to` field
+//! in Rust source code where `reply_target` must be used.
+
+use std::fs;
+use std::path::{Path, PathBuf};
+
+const SCAN_PATHS: &[&str] = &["src", "examples"];
+const FORBIDDEN_PATTERNS: &[&str] = &[".reply_to", "reply_to:"];
+
+fn collect_rs_files(dir: &Path, out: &mut Vec<PathBuf>) {
+    let entries = fs::read_dir(dir)
+        .unwrap_or_else(|err| panic!("Failed to read directory {}: {err}", dir.display()));
+
+    for entry in entries {
+        let entry =
+            entry.unwrap_or_else(|err| panic!("Failed to read entry in {}: {err}", dir.display()));
+        let path = entry.path();
+
+        if path.is_dir() {
+            collect_rs_files(&path, out);
+        } else if path.extension().is_some_and(|ext| ext == "rs") {
+            out.push(path);
+        }
+    }
+}
+
+#[test]
+fn source_does_not_use_legacy_reply_to_field() {
+    let root = Path::new(env!("CARGO_MANIFEST_DIR"));
+    let mut rust_files = Vec::new();
+
+    for relative in SCAN_PATHS {
+        collect_rs_files(&root.join(relative), &mut rust_files);
+    }
+
+    rust_files.sort();
+
+    let mut violations = Vec::new();
+
+    for file_path in rust_files {
+        let content = fs::read_to_string(&file_path).unwrap_or_else(|err| {
+            panic!("Failed to read source file {}: {err}", file_path.display())
+        });
+
+        for (line_idx, line) in content.lines().enumerate() {
+            for pattern in FORBIDDEN_PATTERNS {
+                if line.contains(pattern) {
+                    let rel = file_path
+                        .strip_prefix(root)
+                        .unwrap_or(&file_path)
+                        .display()
+                        .to_string();
+                    violations.push(format!(
+                        "{rel}:{} contains forbidden pattern `{pattern}`: {}",
+                        line_idx + 1,
+                        line.trim()
+                    ));
+                }
+            }
+        }
+    }
+
+    assert!(
+        violations.is_empty(),
+        "Found legacy `reply_to` field usage:\n{}",
+        violations.join("\n")
+    );
+}