feat: Add HTTP status tests and dynamic plugin documentation

- Add e2e_vm_http_status_404/500 tests to verify HTTP status handling
- ResultBox properly returns Ok(Response) for HTTP errors, Err for connection failures
- Create dynamic-plugin-flow.md documenting MIR→VM→Registry→Plugin flow
- Add vm-stats test files for HTTP 404/500 status codes
- Update net-plugin.md with HTTP error handling clarification
- Create E2E_TESTS.md documenting all E2E test behaviors
- Add mir-26-instruction-diet.md for MIR optimization plans
- Add vm-stats-cookbook.md for VM statistics usage guide
- Update MIR verifier to properly track self-assignment patterns

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

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

docs/tools/vm-stats-cookbook.md

@@ -0,0 +1,38 @@
+# VM Stats Cookbook
+
+Collect VM instruction stats (JSON) to guide optimization and instruction set diet.
+
+## Prerequisites
+- Build: `cargo build --release -j32`
+- Ensure plugins are configured in `nyash.toml` if your program uses them.
+
+## Quick Start
+```bash
+# Human-readable
+./target/release/nyash --backend vm --vm-stats local_tests/vm_stats_http_ok.nyash
+
+# JSON for tooling
+./target/release/nyash --backend vm --vm-stats --vm-stats-json local_tests/vm_stats_http_ok.nyash > vm_stats_ok.json
+
+# Or via helper script
+tools/run_vm_stats.sh local_tests/vm_stats_http_ok.nyash vm_stats_ok.json
+```
+
+## Sample Programs
+- `local_tests/vm_stats_http_ok.nyash` — Server responds "OK" to a client GET.
+- `local_tests/vm_stats_http_err.nyash` — Client GET to an unreachable port (Result Err path).
+- `local_tests/vm_stats_http_404.nyash` — Server returns 404/"NF"; transport成功＋アプリ層エラーの代表例。
+- `local_tests/vm_stats_http_500.nyash` — Server returns 500/"ERR"; 同上。
+- `local_tests/vm_stats_filebox.nyash` — FileBox open/write/copyFrom/read.
+
+## Tips
+- Enable plugin debugging when needed:
+  - `NYASH_DEBUG_PLUGIN=1` — Show VM→Plugin TLV header preview.
+  - `NYASH_NET_LOG=1 NYASH_NET_LOG_FILE=net_plugin.log` — Net plugin logs.
+- Env alternative to CLI flags:
+  - `NYASH_VM_STATS=1` and `NYASH_VM_STATS_JSON=1`.
+
+## Next Steps
+- Collect stats for normal and error flows (OK/404/500/unreachable, FileBox)。
+- Compare hot instructions across scenarios（BoxCall/Const/NewBox の比率、Branch/Jump/Phi の有無）。
+- Feed findings into the 26-instruction diet discussion（コア維持・メタ降格・型折りたたみ）。