feat(plugin): Fix plugin BoxRef return and Box argument support

- Fixed deadlock in FileBox plugin copyFrom implementation (single lock)
- Added TLV Handle (tag=8) parsing in calls.rs for returned BoxRefs
- Improved plugin loader with config path consistency and detailed logging
- Fixed loader routing for proper Handle type_id/fini_method_id resolution
- Added detailed logging for TLV encoding/decoding in plugin_loader_v2

Test docs/examples/plugin_boxref_return.nyash now works correctly:
- cloneSelf() returns FileBox Handle properly
- copyFrom(Box) accepts plugin Box arguments
- Both FileBox instances close and fini correctly

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

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

docs/development/proposals/issue_62_update_proposal.md

@@ -0,0 +1,80 @@
+# Issue 62 Update Proposal: Enable String Constants in WASM Backend First
+
+This is a concrete request to implement minimal string support in the WASM backend so that Issue #62 can proceed. It reflects the current repo state.
+
+## Background
+
+- As noted in Issue #61, the current WASM backend does not support string constants yet.
+- Issue #62 depends on string support and cannot be completed without it.
+- Current state:
+  - `src/backend/wasm/codegen.rs` → `generate_const` handles only Integer/Bool/Void; String is not implemented.
+  - `src/backend/wasm/memory.rs` already defines a basic layout for `StringBox`:
+    - Header: `[type_id:i32][ref_count:i32][field_count:i32]`
+    - Fields: `[data_ptr:i32][length:i32]`
+    - `StringBox` type_id = `0x1001`.
+
+## Goal
+
+Add minimal string constant support to the WASM backend:
+
+- Allow `ConstValue::String` in codegen by embedding UTF-8 string bytes and constructing a `StringBox` with `[data_ptr,length]`.
+- Provide a minimal debugging import `env.print_str(ptr,len)` to verify strings at runtime.
+- Unblock Issue #62 implementation and tests that require strings.
+
+## Scope
+
+Minimal features required:
+
+1) Data segments for string literals
+   - Extend `WasmModule` (in `codegen.rs`) with a `data_segments: Vec<String>` field.
+   - Update `to_wat()` to emit `(data ...)` after memory/globals and before functions/exports.
+   - For each string constant, create a unique offset and emit a `(data (i32.const <offset>) "...bytes...")` entry.
+
+2) Codegen for `ConstValue::String`
+   - In `generate_const`, when encountering `ConstValue::String(s)`,
+     - Allocate a data segment for `s` (UTF-8 bytes) and get its offset and length.
+     - Allocate a `StringBox` using existing helpers (see `MemoryManager`),
+       then set its fields: `data_ptr` and `length`.
+     - Return the `StringBox` pointer (i32) in the destination local.
+
+3) Helper for `StringBox` allocation
+   - Either:
+     - Provide a dedicated WAT helper function `$alloc_stringbox` that calls `$malloc`, writes header (`type_id=0x1001`, `ref_count=1`, `field_count=2`), and returns the box pointer, then inline store `data_ptr`/`length`.
+   - Or:
+     - Use `$box_alloc` with `(type_id=0x1001, field_count=2)` and then store `data_ptr`/`length` via generated `i32.store` sequences.
+
+4) Runtime import for string output (for verification)
+   - Extend `RuntimeImports` (`src/backend/wasm/runtime.rs`) with:
+     - `(import "env" "print_str" (func $print_str (param i32 i32)))`
+   - In host (Node/Browser), implement `importObject.env.print_str = (ptr,len) => { decode UTF-8 from memory; console.log(...) }`.
+
+5) E2E test
+   - Add a tiny program that produces/prints a string (e.g., Const String → call `env.print_str(ptr,len)` via a minimal MIR program) and verify it logs the correct text.
+   - Option: update `test_runner.js` to include `print_str` and decode from memory using `TextDecoder('utf-8')`.
+
+## Out of Scope (for this change)
+
+- String operations (concat/substr/compare), normalization, encoding conversions.
+- GC/RC or freeing memory (current allocator is bump-only).
+- Returning StringBox directly from `main` (keep verification via `print_str`).
+
+## Acceptance Criteria
+
+- Generated WAT includes `(data ...)` segments for string literals and correct offsets.
+- `ConstValue::String` codegen constructs a valid `StringBox` with proper `[data_ptr,length]`.
+- `env.print_str` correctly prints UTF-8 strings in both Browser and Node runners.
+- Issue #62 tasks that rely on strings can proceed.
+
+## References (repo paths)
+
+- String unsupported path: `src/backend/wasm/codegen.rs` (`generate_const`)
+- Memory/layout: `src/backend/wasm/memory.rs` (StringBox, type_id=0x1001)
+- Runtime imports: `src/backend/wasm/runtime.rs` (currently only `env.print(i32)`)
+- Node runner: `test_runner.js` (has `env.print`; extend with `print_str`)
+
+## Notes
+
+- Data segment approach is the simplest for initial support; future work may add constant pooling and deduplication.
+- Keeping verification via `print_str(ptr,len)` avoids complicating function return types for now.
+- UTF-8 decoding is available in hosts via `TextDecoder('utf-8')`.
+