feat: Add parallel HTTP server E2E tests and enhance plugin system

- Add e2e_plugin_net_additional.rs with parallel server tests
- Fix test to properly handle request objects (no double accept)
- Add comprehensive net-plugin documentation
- Implement debug tracing for method calls
- Enhance plugin lifecycle documentation
- Improve error handling in plugin loader
- Add leak tracking infrastructure (for future use)
- Update language spec with latest plugin features

This enhances test coverage for concurrent HTTP servers and improves
the overall plugin system documentation and debugging capabilities.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

tests/e2e_plugin_net_additional.rs

@@ -0,0 +1,99 @@
+#![cfg(all(feature = "plugins", not(target_arch = "wasm32")))]
+
+use nyash_rust::parser::NyashParser;
+use nyash_rust::runtime::plugin_loader_v2::{init_global_loader_v2, get_global_loader_v2};
+use nyash_rust::runtime::box_registry::get_global_registry;
+use nyash_rust::runtime::PluginConfig;
+
+fn try_init_plugins() -> bool {
+    if !std::path::Path::new("nyash.toml").exists() { return false; }
+    if let Err(e) = init_global_loader_v2("nyash.toml") { eprintln!("init failed: {:?}", e); return false; }
+    let loader = get_global_loader_v2();
+    let loader = loader.read().unwrap();
+    if let Some(conf) = &loader.config {
+        let mut map = std::collections::HashMap::new();
+        for (lib, def) in &conf.libraries { for b in &def.boxes { map.insert(b.clone(), lib.clone()); } }
+        get_global_registry().apply_plugin_config(&PluginConfig { plugins: map });
+        true
+    } else { false }
+}
+
+#[test]
+fn e2e_http_two_servers_parallel() {
+    std::env::set_var("NYASH_NET_LOG", "1");
+    std::env::set_var("NYASH_NET_LOG_FILE", "net_plugin.log");
+    if !try_init_plugins() { return; }
+
+    let code = r#"
+local s1, s2, c, r1, r2, req1, req2, p1, p2, x, y
+s1 = new HttpServerBox()
+s2 = new HttpServerBox()
+s1.start(8101)
+s2.start(8102)
+
+c = new HttpClientBox()
+r1 = c.get("http://localhost:8101/a")
+r2 = c.get("http://localhost:8102/b")
+
+// accept once per pending request and keep handles
+req1 = s1.accept()
+req2 = s2.accept()
+p1 = req1.path()
+p2 = req2.path()
+
+x = new HttpResponseBox()
+x.write("X")
+y = new HttpResponseBox()
+y.write("Y")
+
+// respond using kept request handles
+req1.respond(x)
+req2.respond(y)
+
+// read results
+x = r1.readBody()
+y = r2.readBody()
+x + ":" + y
+"#;
+
+    let ast = NyashParser::parse_from_string(code).expect("parse");
+    let mut i = nyash_rust::interpreter::NyashInterpreter::new();
+    let result = i.execute(ast).expect("exec");
+    assert!(result.to_string_box().value.contains(":"));
+}
+
+#[test]
+fn e2e_http_long_body_and_headers() {
+    std::env::set_var("NYASH_NET_LOG", "1");
+    std::env::set_var("NYASH_NET_LOG_FILE", "net_plugin.log");
+    if !try_init_plugins() { return; }
+
+    let code = r#"
+local s, c, r, q, resp, body, hv
+s = new HttpServerBox()
+s.start(8103)
+
+c = new HttpClientBox()
+r = c.post("http://localhost:8103/long", "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa")
+
+q = s.accept()
+body = q.readBody()
+resp = new HttpResponseBox()
+resp.setStatus(202)
+resp.setHeader("X-Alpha", "A")
+resp.setHeader("X-Beta", "B")
+resp.write("OK-LONG")
+q.respond(resp)
+
+body = r.readBody()
+hv = r.getHeader("X-Alpha")
+hv + ":" + body
+"#;
+
+    let ast = NyashParser::parse_from_string(code).expect("parse");
+    let mut i = nyash_rust::interpreter::NyashInterpreter::new();
+    let result = i.execute(ast).expect("exec");
+    let s = result.to_string_box().value;
+    assert!(s.starts_with("A:"));
+    assert!(s.contains("OK-LONG"));
+}