diff --git a/src/mir/builder/control_flow/joinir/patterns/mod.rs b/src/mir/builder/control_flow/joinir/patterns/mod.rs
index 1ff0aa9f..8fc40e75 100644
--- a/src/mir/builder/control_flow/joinir/patterns/mod.rs
+++ b/src/mir/builder/control_flow/joinir/patterns/mod.rs
@@ -60,6 +60,7 @@ pub(in crate::mir::builder) mod escape_pattern_recognizer; // Phase 91 P5b
 pub(in crate::mir::builder) mod common_init;
 pub(in crate::mir::builder) mod loop_true_counter_extractor; // Phase 104: loop(true) counter extraction for Pattern2
 pub(in crate::mir::builder) mod read_digits_break_condition_box; // Phase 104: break cond normalization for read_digits(loop(true))
+pub(in crate::mir::builder) mod pattern2; // Phase 263 P0.2: Pattern2 module (api/ SSOT entry point)
 pub(in crate::mir::builder) mod pattern2_break_condition_policy_router; // Phase 105: policy router box for Pattern2 break condition
 pub(in crate::mir::builder) mod pattern2_policy_router; // Phase 108: unified Pattern2 policy router (balanced/read_digits/default)
 pub(in crate::mir::builder) mod pattern2_inputs_facts_box; // Phase 105: Pattern2 input facts (analysis only)
diff --git a/src/mir/builder/control_flow/joinir/patterns/pattern2/api/mod.rs b/src/mir/builder/control_flow/joinir/patterns/pattern2/api/mod.rs
new file mode 100644
index 00000000..f89236b8
--- /dev/null
+++ b/src/mir/builder/control_flow/joinir/patterns/pattern2/api/mod.rs
@@ -0,0 +1,23 @@
+//! Phase 263 P0.2: Pattern2 promotion API (entry point SSOT)
+//!
+//! This module is the single entry point for Pattern2 promotion logic.
+//! All callers should use this module's exports instead of accessing internals.
+//!
+//! # Usage
+//!
+//! ```ignore
+//! use super::pattern2::api::{try_promote, PromoteDecision};
+//!
+//! match try_promote(builder, condition, body, inputs, debug, verbose)? {
+//!     PromoteDecision::Promoted(result) => { /* ... */ }
+//!     PromoteDecision::NotApplicable => { /* fallback to next path */ }
+//!     PromoteDecision::Freeze(reason) => { /* fail-fast */ }
+//! }
+//! ```
+
+mod promote_decision;
+mod promote_runner;
+
+// Re-export the SSOT types and functions
+pub(in crate::mir::builder) use promote_decision::{PromoteDecision, PromoteStepResult};
+pub(in crate::mir::builder) use promote_runner::try_promote;
diff --git a/src/mir/builder/control_flow/joinir/patterns/pattern2/api/promote_decision.rs b/src/mir/builder/control_flow/joinir/patterns/pattern2/api/promote_decision.rs
new file mode 100644
index 00000000..b92e5948
--- /dev/null
+++ b/src/mir/builder/control_flow/joinir/patterns/pattern2/api/promote_decision.rs
@@ -0,0 +1,26 @@
+//! Phase 263 P0.2: Promotion decision types (SSOT)
+//!
+//! PromoteDecision enum eliminates Option<_> wrapping ambiguity by making
+//! the decision explicit. All Pattern2 promotion logic flows through this type.
+
+use super::super::super::pattern2_inputs_facts_box::Pattern2Inputs;
+
+pub(crate) struct PromoteStepResult {
+    pub inputs: Pattern2Inputs,
+}
+
+/// Phase 263 P0.1: Promotion decision for Pattern2 LoopBodyLocal handling
+///
+/// Eliminates Option<_> wrapping ambiguity by making decision explicit.
+pub(crate) enum PromoteDecision {
+    /// Promotion succeeded - Pattern2 can proceed
+    Promoted(PromoteStepResult),
+
+    /// Pattern2 not applicable (e.g., reassigned LoopBodyLocal, no promotable pattern)
+    /// → Router should try next path (legacy binding, etc.)
+    NotApplicable,
+
+    /// Pattern2 should handle this but implementation is missing
+    /// → Fail-Fast with error message
+    Freeze(String),
+}
diff --git a/src/mir/builder/control_flow/joinir/patterns/pattern2/api/promote_runner.rs b/src/mir/builder/control_flow/joinir/patterns/pattern2/api/promote_runner.rs
new file mode 100644
index 00000000..aa9b44a9
--- /dev/null
+++ b/src/mir/builder/control_flow/joinir/patterns/pattern2/api/promote_runner.rs
@@ -0,0 +1,180 @@
+//! Phase 263 P0.2: Pattern2 promotion runner (SSOT entry point)
+//!
+//! Single entry point for all Pattern2 promotion logic.
+//! All callers should use `try_promote()` instead of accessing internals directly.
+
+use crate::ast::ASTNode;
+use crate::mir::builder::MirBuilder;
+
+use super::super::super::body_local_policy::{classify_for_pattern2, BodyLocalRoute};
+use super::super::super::pattern2_inputs_facts_box::Pattern2Inputs;
+use super::super::super::policies::PolicyDecision;
+
+use super::promote_decision::{PromoteDecision, PromoteStepResult};
+
+/// Phase 263 P0.2: Try to promote LoopBodyLocal variables for Pattern2
+///
+/// This is the single entry point for Pattern2 promotion logic.
+/// Returns PromoteDecision to indicate success, applicability, or freeze.
+pub(in crate::mir::builder) fn try_promote(
+    builder: &mut MirBuilder,
+    condition: &ASTNode,
+    body: &[ASTNode],
+    inputs: Pattern2Inputs,
+    debug: bool,
+    verbose: bool,
+) -> Result<PromoteDecision, String> {
+    let mut inputs = inputs;
+    use crate::mir::join_ir::lowering::digitpos_condition_normalizer::DigitPosConditionNormalizer;
+    use crate::mir::loop_pattern_detection::loop_condition_scope::LoopConditionScopeBox;
+
+    let cond_scope = LoopConditionScopeBox::analyze(
+        &inputs.loop_var_name,
+        &vec![condition, &inputs.break_condition_node],
+        Some(&inputs.scope),
+    );
+
+    let mut promoted_pairs: Vec<(String, String)> = Vec::new();
+    let cond_body_local_vars: Vec<String> = cond_scope
+        .vars
+        .iter()
+        .filter(|v| matches!(v.scope, crate::mir::loop_pattern_detection::loop_condition_scope::CondVarScope::LoopBodyLocal))
+        .map(|v| v.name.clone())
+        .collect();
+
+    if cond_scope.has_loop_body_local() {
+        // Policy-controlled: some families must not run promotion/slot heuristics here.
+        // Example: balanced depth-scan uses derived vars and doesn't have a break-guard node.
+        if matches!(
+            inputs.body_local_handling,
+            crate::mir::builder::control_flow::joinir::patterns::pattern2_inputs_facts_box::BodyLocalHandlingPolicy::SkipPromotion
+        ) {
+            // no-op: lowerers will populate LoopBodyLocalEnv via init/derived emission.
+        } else if !inputs.is_loop_true_read_digits {
+            match classify_for_pattern2(
+                builder,
+                &inputs.loop_var_name,
+                &inputs.scope,
+                &inputs.break_condition_node,
+                &cond_scope,
+                body,
+            ) {
+                PolicyDecision::Use(BodyLocalRoute::Promotion {
+                    promoted_carrier,
+                    promoted_var,
+                    carrier_name,
+                }) => {
+                    let is_trim_promotion = promoted_carrier.trim_helper().is_some();
+                    if !is_trim_promotion {
+                        promoted_pairs.push((promoted_var.clone(), carrier_name.clone()));
+                    }
+
+                    #[cfg(feature = "normalized_dev")]
+                    {
+                        use crate::mir::join_ir::lowering::carrier_binding_assigner::CarrierBindingAssigner;
+                        let mut promoted_carrier = promoted_carrier;
+                        CarrierBindingAssigner::assign_promoted_binding(
+                            builder,
+                            &mut promoted_carrier,
+                            &promoted_var,
+                            &carrier_name,
+                        )
+                        .map_err(|e| format!("[phase78/binding_assign] {:?}", e))?;
+                        inputs.carrier_info.merge_from(&promoted_carrier);
+                    }
+                    #[cfg(not(feature = "normalized_dev"))]
+                    {
+                        inputs.carrier_info.merge_from(&promoted_carrier);
+                    }
+
+                    inputs
+                        .carrier_info
+                        .promoted_loopbodylocals
+                        .push(promoted_var.clone());
+
+                    if !is_trim_promotion {
+                        inputs.break_condition_node = DigitPosConditionNormalizer::normalize(
+                            &inputs.break_condition_node,
+                            &promoted_var,
+                            &carrier_name,
+                        );
+                    }
+                }
+                PolicyDecision::Use(BodyLocalRoute::ReadOnlySlot(slot)) => {
+                    inputs.allowed_body_locals_for_conditions = vec![slot.name.clone()];
+                    inputs.read_only_body_local_slot = Some(slot);
+                }
+                PolicyDecision::Reject(reason) => {
+                    // Phase 263 P0.1: Reject を PromoteDecision で二分化（型安全）
+                    if reason.contains("not_readonly")
+                        || reason.contains("No promotable pattern detected")
+                    {
+                        // 対象外: Pattern2 で処理できない形 → NotApplicable で後続経路へ
+                        #[cfg(debug_assertions)]
+                        {
+                            eprintln!(
+                                "[pattern2/api/promote] Pattern2 対象外（LoopBodyLocal {:?}）: {}. 後続経路へfallback.",
+                                cond_body_local_vars, reason
+                            );
+                        }
+                        return Ok(PromoteDecision::NotApplicable);
+                    } else {
+                        // 対象だが未対応（freeze級）: 実装バグ or 将来実装予定 → Freeze で Fail-Fast
+                        return Ok(PromoteDecision::Freeze(format!(
+                            "[pattern2/api/promote] Pattern2 未対応エラー（LoopBodyLocal {:?}）: {}",
+                            cond_body_local_vars, reason
+                        )));
+                    }
+                }
+                PolicyDecision::None => {}
+            }
+        }
+    }
+
+    // Allocate join_ids for carriers and register bindings.
+    for carrier in &mut inputs.carrier_info.carriers {
+        let carrier_join_id = inputs.join_value_space.alloc_param();
+        carrier.join_id = Some(carrier_join_id);
+        #[cfg(feature = "normalized_dev")]
+        if let Some(binding_id) = carrier.binding_id {
+            use crate::mir::join_ir::lowering::carrier_info::CarrierRole;
+            match carrier.role {
+                CarrierRole::ConditionOnly => inputs.env.register_condition_binding(binding_id, carrier_join_id),
+                CarrierRole::LoopState => inputs.env.register_carrier_binding(binding_id, carrier_join_id),
+            }
+        }
+    }
+
+    for (promoted_var, promoted_carrier_name) in promoted_pairs {
+        let join_id = inputs
+            .carrier_info
+            .find_carrier(&promoted_carrier_name)
+            .and_then(|c| c.join_id)
+            .ok_or_else(|| format!("[phase229] promoted carrier '{}' has no join_id", promoted_carrier_name))?;
+        inputs.env.insert(promoted_var, join_id);
+    }
+
+    // ExprLowerer validation (best-effort; unchanged behavior)
+    {
+        use crate::mir::join_ir::lowering::expr_lowerer::{ExprContext, ExprLowerer, ExprLoweringError};
+        use crate::mir::join_ir::lowering::scope_manager::Pattern2ScopeManager;
+
+        let scope_manager = Pattern2ScopeManager {
+            condition_env: &inputs.env,
+            loop_body_local_env: Some(&inputs.body_local_env),
+            captured_env: Some(&inputs.captured_env),
+            carrier_info: &inputs.carrier_info,
+        };
+
+        match ExprLowerer::new(&scope_manager, ExprContext::Condition, builder)
+            .with_debug(debug)
+            .lower(&inputs.break_condition_node)
+        {
+            Ok(_) => {}
+            Err(ExprLoweringError::UnsupportedNode(_)) => {}
+            Err(_) => {}
+        }
+    }
+
+    Ok(PromoteDecision::Promoted(PromoteStepResult { inputs }))
+}
diff --git a/src/mir/builder/control_flow/joinir/patterns/pattern2/mod.rs b/src/mir/builder/control_flow/joinir/patterns/pattern2/mod.rs
new file mode 100644
index 00000000..9a95cc4b
--- /dev/null
+++ b/src/mir/builder/control_flow/joinir/patterns/pattern2/mod.rs
@@ -0,0 +1,6 @@
+//! Phase 263 P0.2: Pattern2 module structure
+//!
+//! This module organizes Pattern2 logic with a clear SSOT structure:
+//! - `api/` - Public entry point for promotion logic (SSOT)
+
+pub(in crate::mir::builder) mod api;
diff --git a/src/mir/builder/control_flow/joinir/patterns/pattern2_lowering_orchestrator.rs b/src/mir/builder/control_flow/joinir/patterns/pattern2_lowering_orchestrator.rs
index 5003bca7..bd4d24da 100644
--- a/src/mir/builder/control_flow/joinir/patterns/pattern2_lowering_orchestrator.rs
+++ b/src/mir/builder/control_flow/joinir/patterns/pattern2_lowering_orchestrator.rs
@@ -62,9 +62,9 @@ impl Pattern2LoweringOrchestrator {
         let facts = GatherFactsStepBox::gather(builder, condition, body, fn_body, &ctx, verbose)?;
         let inputs = ApplyPolicyStepBox::apply(condition, body, facts)?;
 
-        // Phase 263 P0.1: PromoteDecision で分岐を1箇所に固定（型安全）
-        use super::pattern2_steps::promote_step_box::PromoteDecision;
-        let mut inputs = match PromoteStepBox::run(builder, condition, body, inputs, debug, verbose)? {
+        // Phase 263 P0.2: pattern2::api 経由で try_promote を呼び出し（入口SSOT）
+        use super::pattern2::api::{try_promote, PromoteDecision};
+        let mut inputs = match try_promote(builder, condition, body, inputs, debug, verbose)? {
             PromoteDecision::Promoted(result) => {
                 result.inputs
             }
diff --git a/src/mir/builder/control_flow/joinir/patterns/pattern2_steps/promote_step_box.rs b/src/mir/builder/control_flow/joinir/patterns/pattern2_steps/promote_step_box.rs
index 26c7c9fa..569ad0ce 100644
--- a/src/mir/builder/control_flow/joinir/patterns/pattern2_steps/promote_step_box.rs
+++ b/src/mir/builder/control_flow/joinir/patterns/pattern2_steps/promote_step_box.rs
@@ -1,40 +1,24 @@
 //! PromoteStepBox (Phase 106)
 //!
+//! Phase 263 P0.2: This is now a thin wrapper over pattern2::api::try_promote.
+//! All promotion logic has been moved to pattern2::api for SSOT.
+//!
 //! Responsibility:
-//! - promotion / read-only slot routing for body-local vars in conditions
-//! - carrier preparation for JoinIR emission
+//! - Backward compatibility wrapper for existing callers
+//! - Delegates to pattern2::api::try_promote for actual implementation
 
 use crate::ast::ASTNode;
 use crate::mir::builder::MirBuilder;
-use crate::mir::loop_pattern_detection::error_messages;
 
-use super::super::body_local_policy::{classify_for_pattern2, BodyLocalRoute};
+use super::super::pattern2::api::{try_promote, PromoteDecision, PromoteStepResult};
 use super::super::pattern2_inputs_facts_box::Pattern2Inputs;
-use super::super::policies::PolicyDecision;
-
-pub(crate) struct PromoteStepResult {
-    pub inputs: Pattern2Inputs,
-}
-
-/// Phase 263 P0.1: Promotion decision for Pattern2 LoopBodyLocal handling
-///
-/// Eliminates Option<_> wrapping ambiguity by making decision explicit.
-pub(crate) enum PromoteDecision {
-    /// Promotion succeeded - Pattern2 can proceed
-    Promoted(PromoteStepResult),
-
-    /// Pattern2 not applicable (e.g., reassigned LoopBodyLocal, no promotable pattern)
-    /// → Router should try next path (legacy binding, etc.)
-    NotApplicable,
-
-    /// Pattern2 should handle this but implementation is missing
-    /// → Fail-Fast with error message
-    Freeze(String),
-}
 
 pub(crate) struct PromoteStepBox;
 
 impl PromoteStepBox {
+    /// Phase 263 P0.2: Thin wrapper over pattern2::api::try_promote
+    ///
+    /// This method is deprecated. Use pattern2::api::try_promote directly.
     pub(crate) fn run(
         builder: &mut MirBuilder,
         condition: &ASTNode,
@@ -43,170 +27,6 @@ impl PromoteStepBox {
         debug: bool,
         verbose: bool,
     ) -> Result<PromoteDecision, String> {
-        Self::promote_and_prepare_carriers(builder, condition, body, inputs, debug, verbose)
+        try_promote(builder, condition, body, inputs, debug, verbose)
     }
-
-    pub(in crate::mir::builder) fn promote_and_prepare_carriers(
-        builder: &mut MirBuilder,
-        condition: &ASTNode,
-        body: &[ASTNode],
-        inputs: Pattern2Inputs,
-        debug: bool,
-        verbose: bool,
-    ) -> Result<PromoteDecision, String> {
-        let mut inputs = inputs;
-        use crate::mir::join_ir::lowering::digitpos_condition_normalizer::DigitPosConditionNormalizer;
-        use crate::mir::loop_pattern_detection::loop_condition_scope::LoopConditionScopeBox;
-
-        let cond_scope = LoopConditionScopeBox::analyze(
-            &inputs.loop_var_name,
-            &vec![condition, &inputs.break_condition_node],
-            Some(&inputs.scope),
-        );
-
-        let mut promoted_pairs: Vec<(String, String)> = Vec::new();
-        let cond_body_local_vars: Vec<String> = cond_scope
-            .vars
-            .iter()
-            .filter(|v| matches!(v.scope, crate::mir::loop_pattern_detection::loop_condition_scope::CondVarScope::LoopBodyLocal))
-            .map(|v| v.name.clone())
-            .collect();
-
-        if cond_scope.has_loop_body_local() {
-            // Policy-controlled: some families must not run promotion/slot heuristics here.
-            // Example: balanced depth-scan uses derived vars and doesn't have a break-guard node.
-            if matches!(
-                inputs.body_local_handling,
-                crate::mir::builder::control_flow::joinir::patterns::pattern2_inputs_facts_box::BodyLocalHandlingPolicy::SkipPromotion
-            ) {
-                // no-op: lowerers will populate LoopBodyLocalEnv via init/derived emission.
-            } else if !inputs.is_loop_true_read_digits {
-                match classify_for_pattern2(
-                    builder,
-                    &inputs.loop_var_name,
-                    &inputs.scope,
-                    &inputs.break_condition_node,
-                    &cond_scope,
-                    body,
-                ) {
-                    PolicyDecision::Use(BodyLocalRoute::Promotion {
-                        promoted_carrier,
-                        promoted_var,
-                        carrier_name,
-                    }) => {
-                        let is_trim_promotion = promoted_carrier.trim_helper().is_some();
-                        if !is_trim_promotion {
-                            promoted_pairs.push((promoted_var.clone(), carrier_name.clone()));
-                        }
-
-                        #[cfg(feature = "normalized_dev")]
-                        {
-                            use crate::mir::join_ir::lowering::carrier_binding_assigner::CarrierBindingAssigner;
-                            let mut promoted_carrier = promoted_carrier;
-                            CarrierBindingAssigner::assign_promoted_binding(
-                                builder,
-                                &mut promoted_carrier,
-                                &promoted_var,
-                                &carrier_name,
-                            )
-                            .map_err(|e| format!("[phase78/binding_assign] {:?}", e))?;
-                            inputs.carrier_info.merge_from(&promoted_carrier);
-                        }
-                        #[cfg(not(feature = "normalized_dev"))]
-                        {
-                            inputs.carrier_info.merge_from(&promoted_carrier);
-                        }
-
-                        inputs
-                            .carrier_info
-                            .promoted_loopbodylocals
-                            .push(promoted_var.clone());
-
-                        if !is_trim_promotion {
-                            inputs.break_condition_node = DigitPosConditionNormalizer::normalize(
-                                &inputs.break_condition_node,
-                                &promoted_var,
-                                &carrier_name,
-                            );
-                        }
-                    }
-                    PolicyDecision::Use(BodyLocalRoute::ReadOnlySlot(slot)) => {
-                        inputs.allowed_body_locals_for_conditions = vec![slot.name.clone()];
-                        inputs.read_only_body_local_slot = Some(slot);
-                    }
-                    PolicyDecision::Reject(reason) => {
-                        // Phase 263 P0.1: Reject を PromoteDecision で二分化（型安全）
-                        if reason.contains("not_readonly")
-                            || reason.contains("No promotable pattern detected")
-                        {
-                            // 対象外: Pattern2 で処理できない形 → NotApplicable で後続経路へ
-                            #[cfg(debug_assertions)]
-                            {
-                                eprintln!(
-                                    "[pattern2/promote_step] Pattern2 対象外（LoopBodyLocal {:?}）: {}. 後続経路へfallback.",
-                                    cond_body_local_vars, reason
-                                );
-                            }
-                            return Ok(PromoteDecision::NotApplicable);
-                        } else {
-                            // 対象だが未対応（freeze級）: 実装バグ or 将来実装予定 → Freeze で Fail-Fast
-                            return Ok(PromoteDecision::Freeze(format!(
-                                "[pattern2/promote_step] Pattern2 未対応エラー（LoopBodyLocal {:?}）: {}",
-                                cond_body_local_vars, reason
-                            )));
-                        }
-                    }
-                    PolicyDecision::None => {}
-                }
-            }
-        }
-
-        // Allocate join_ids for carriers and register bindings.
-        for carrier in &mut inputs.carrier_info.carriers {
-            let carrier_join_id = inputs.join_value_space.alloc_param();
-            carrier.join_id = Some(carrier_join_id);
-            #[cfg(feature = "normalized_dev")]
-            if let Some(binding_id) = carrier.binding_id {
-                use crate::mir::join_ir::lowering::carrier_info::CarrierRole;
-                match carrier.role {
-                    CarrierRole::ConditionOnly => inputs.env.register_condition_binding(binding_id, carrier_join_id),
-                    CarrierRole::LoopState => inputs.env.register_carrier_binding(binding_id, carrier_join_id),
-                }
-            }
-        }
-
-        for (promoted_var, promoted_carrier_name) in promoted_pairs {
-            let join_id = inputs
-                .carrier_info
-                .find_carrier(&promoted_carrier_name)
-                .and_then(|c| c.join_id)
-                .ok_or_else(|| format!("[phase229] promoted carrier '{}' has no join_id", promoted_carrier_name))?;
-            inputs.env.insert(promoted_var, join_id);
-        }
-
-        // ExprLowerer validation (best-effort; unchanged behavior)
-        {
-            use crate::mir::join_ir::lowering::expr_lowerer::{ExprContext, ExprLowerer, ExprLoweringError};
-            use crate::mir::join_ir::lowering::scope_manager::Pattern2ScopeManager;
-
-            let scope_manager = Pattern2ScopeManager {
-                condition_env: &inputs.env,
-                loop_body_local_env: Some(&inputs.body_local_env),
-                captured_env: Some(&inputs.captured_env),
-                carrier_info: &inputs.carrier_info,
-            };
-
-            match ExprLowerer::new(&scope_manager, ExprContext::Condition, builder)
-                .with_debug(debug)
-                .lower(&inputs.break_condition_node)
-            {
-                Ok(_) => {}
-                Err(ExprLoweringError::UnsupportedNode(_)) => {}
-                Err(_) => {}
-            }
-        }
-
-        Ok(PromoteDecision::Promoted(PromoteStepResult { inputs }))
-    }
-
 }