diff --git a/src/config/env/joinir_dev.rs b/src/config/env/joinir_dev.rs
index e5164fd8..eb29cdea 100644
--- a/src/config/env/joinir_dev.rs
+++ b/src/config/env/joinir_dev.rs
@@ -48,3 +48,53 @@ pub fn snapshot_test_enabled() -> bool {
 pub fn input_mode() -> Option<String> {
     std::env::var("NYASH_JOINIR_INPUT").ok()
 }
+
+/// NYASH_JOINIR_LOWER_FROM_MIR=1 - Enable lowering from MIR mode
+pub fn lower_from_mir_enabled() -> bool {
+    env_bool("NYASH_JOINIR_LOWER_FROM_MIR")
+}
+
+/// NYASH_JOINIR_LLVM_EXPERIMENT=1 - LLVM experimental mode
+pub fn llvm_experiment_enabled() -> bool {
+    env_bool("NYASH_JOINIR_LLVM_EXPERIMENT")
+}
+
+/// HAKO_JOINIR_IF_TOPLEVEL=1 - Enable If-select for top-level if statements
+pub fn if_toplevel_enabled() -> bool {
+    env_bool("HAKO_JOINIR_IF_TOPLEVEL")
+}
+
+/// HAKO_JOINIR_IF_TOPLEVEL_TRACE=1 - Debug trace for top-level if
+pub fn if_toplevel_trace_enabled() -> bool {
+    env_bool("HAKO_JOINIR_IF_TOPLEVEL_TRACE")
+}
+
+/// HAKO_JOINIR_IF_IN_LOOP_TRACE=1 - Debug trace for if in loop
+pub fn if_in_loop_trace_enabled() -> bool {
+    env_bool("HAKO_JOINIR_IF_IN_LOOP_TRACE")
+}
+
+/// HAKO_JOINIR_NESTED_IF=1 - Enable nested if lowering
+pub fn nested_if_enabled() -> bool {
+    env_bool("HAKO_JOINIR_NESTED_IF")
+}
+
+/// HAKO_JOINIR_PRINT_TOKENS_MAIN=1 - Print tokens for main
+pub fn print_tokens_main_enabled() -> bool {
+    env_bool("HAKO_JOINIR_PRINT_TOKENS_MAIN")
+}
+
+/// HAKO_JOINIR_ARRAY_FILTER_MAIN=1 - Array filter main mode
+pub fn array_filter_main_enabled() -> bool {
+    env_bool("HAKO_JOINIR_ARRAY_FILTER_MAIN")
+}
+
+/// HAKO_JOINIR_READ_QUOTED=1 - Read quoted mode
+pub fn read_quoted_enabled() -> bool {
+    env_bool("HAKO_JOINIR_READ_QUOTED")
+}
+
+/// HAKO_JOINIR_READ_QUOTED_IFMERGE=1 - Read quoted with if-merge
+pub fn read_quoted_ifmerge_enabled() -> bool {
+    env_bool("HAKO_JOINIR_READ_QUOTED_IFMERGE")
+}
diff --git a/src/mir/join_ir/mod.rs b/src/mir/join_ir/mod.rs
index 1d0be9d0..50399b28 100644
--- a/src/mir/join_ir/mod.rs
+++ b/src/mir/join_ir/mod.rs
@@ -102,8 +102,32 @@ impl JoinContId {
 pub type VarId = ValueId;
 
 /// 環境変数フラグが "1" かチェックするヘルパー（JoinIR 実験経路用）
+/// Phase 72-C Step 2: SSOT統一 - すべてのリードを config::env::joinir_dev 経由に
 pub(crate) fn env_flag_is_1(name: &str) -> bool {
-    std::env::var(name).ok().as_deref() == Some("1")
+    use crate::config::env::joinir_dev;
+    match name {
+        "NYASH_JOINIR_LOWER_GENERIC" => joinir_dev::lower_generic_enabled(),
+        "NYASH_JOINIR_MAINLINE_DEBUG" => joinir_dev::mainline_debug_enabled(),
+        "NYASH_JOINIR_IF_MERGE" => joinir_dev::if_merge_enabled(),
+        "NYASH_JOINIR_DEBUG" => joinir_dev::debug_enabled(),
+        "NYASH_JOINIR_VM_BRIDGE" => joinir_dev::vm_bridge_enabled(),
+        "NYASH_JOINIR_STRICT" => joinir_dev::strict_enabled(),
+        "NYASH_JOINIR_SNAPSHOT_GENERATE" => joinir_dev::snapshot_generate_enabled(),
+        "NYASH_JOINIR_SNAPSHOT_TEST" => joinir_dev::snapshot_test_enabled(),
+        "NYASH_JOINIR_LOWER_FROM_MIR" => joinir_dev::lower_from_mir_enabled(),
+        "NYASH_JOINIR_LLVM_EXPERIMENT" => joinir_dev::llvm_experiment_enabled(),
+        "HAKO_JOINIR_IF_TOPLEVEL" => joinir_dev::if_toplevel_enabled(),
+        "HAKO_JOINIR_IF_TOPLEVEL_TRACE" => joinir_dev::if_toplevel_trace_enabled(),
+        "HAKO_JOINIR_IF_IN_LOOP_TRACE" => joinir_dev::if_in_loop_trace_enabled(),
+        "HAKO_JOINIR_NESTED_IF" => joinir_dev::nested_if_enabled(),
+        "HAKO_JOINIR_PRINT_TOKENS_MAIN" => joinir_dev::print_tokens_main_enabled(),
+        "HAKO_JOINIR_ARRAY_FILTER_MAIN" => joinir_dev::array_filter_main_enabled(),
+        "HAKO_JOINIR_READ_QUOTED" => joinir_dev::read_quoted_enabled(),
+        "HAKO_JOINIR_READ_QUOTED_IFMERGE" => joinir_dev::read_quoted_ifmerge_enabled(),
+        // Fallback for unknown flags (shouldn't happen in normal operation)
+        // NYASH_JOINIR_EXPERIMENT is handled by test helpers, not body code
+        _ => std::env::var(name).ok().as_deref() == Some("1"),
+    }
 }
 
 /// Phase 27.4-A: ループ header φ の意味を表す構造（Pinned/Carrier 分類）