restore(lang/compiler): bring back lang/src/compiler from e917d400; add Hako index canaries and docs; implement Rust-side index operator (Array/Map get/set) with Fail‑Fast diagnostics

- restore: lang/src/compiler/** (parser/emit/builder/pipeline_v2) from e917d400
- docs: docs/development/selfhosting/index-operator-hako.md
- smokes(hako): tools/smokes/v2/profiles/quick/core/index_operator_hako.sh (opt-in)
- smokes(vm): adjust index_operator_vm.sh for semicolon gate + stable error text
- rust/parser: allow IndexExpr and assignment LHS=Index; postfix parse LBRACK chain
- rust/builder: lower arr/map index to BoxCall get/set; annotate array/map literals; Fail‑Fast for unsupported types
- CURRENT_TASK: mark Rust side done; add Hako tasks checklist

Note: files disappeared likely due to branch FF to a lineage without lang/src/compiler; no explicit delete commit found. Added anchor checks and suggested CI guard in follow-up.

crates/nyash_kernel/src/lib.rs

@@ -234,7 +234,7 @@ pub extern "C" fn nyash_box_from_i64(val: i64) -> i64 {
 pub extern "C" fn nyash_env_box_new(type_name: *const i8) -> i64 {
     use nyash_rust::{
         box_trait::NyashBox,
-        runtime::{host_handles as handles, box_registry::get_global_registry},
+        runtime::{box_registry::get_global_registry, host_handles as handles},
     };
     use std::ffi::CStr;
     if type_name.is_null() {
@@ -283,7 +283,7 @@ pub extern "C" fn nyash_env_box_new_i64x(
 ) -> i64 {
     use nyash_rust::{
         box_trait::{IntegerBox, NyashBox},
-        runtime::{host_handles as handles, box_registry::get_global_registry},
+        runtime::{box_registry::get_global_registry, host_handles as handles},
     };
     use std::ffi::CStr;
     if type_name.is_null() {
@@ -353,7 +353,7 @@ pub extern "C" fn nyash_any_length_h_export(handle: i64) -> i64 {
     use nyash_rust::runtime::host_handles as handles;
     if std::env::var("NYASH_JIT_TRACE_LEN").ok().as_deref() == Some("1") {
         let present = if handle > 0 {
-                handles::get(handle as u64).is_some()
+            handles::get(handle as u64).is_some()
         } else {
             false
         };