feat(joinir): Phase 188 Pattern 1 Core Implementation + Phase 189 Planning

Phase 188 Status: Planning & Foundation Complete (100%)

Completed Tasks:
✅ Task 188-1: Error Inventory (5 patterns identified)
✅ Task 188-2: Pattern Classification (3 patterns selected)
✅ Task 188-3: Design (51KB comprehensive blueprint)
✅ Task 188-4: Implementation Foundation (1,802 lines scaffolding)
✅ Task 188-5: Verification & Documentation
✅ Pattern 1 Core Implementation: Detection + Lowering + Routing

Pattern 1 Implementation (322 lines):
- Pattern Detection: is_simple_while_pattern() in loop_pattern_detection.rs
- JoinIR Lowering: lower_simple_while_to_joinir() in simple_while_minimal.rs (219 lines)
  - Generates 3 functions: entry, loop_step (tail-recursive), k_exit
  - Implements condition negation: exit_cond = !(i < 3)
  - Tail-recursive Call pattern with state propagation
- Routing: Added "main" to function routing list in control_flow.rs
- Build: ✅ SUCCESS (0 errors, 34 warnings)

Infrastructure Blocker Identified:
- merge_joinir_mir_blocks() only handles single-function JoinIR modules
- Pattern 1 generates 3 functions (entry + loop_step + k_exit)
- Current implementation only merges first function → loop body never executes
- Root cause: control_flow.rs line ~850 takes only .next() function

Phase 189 Planning Complete:
- Goal: Refactor merge_joinir_mir_blocks() for multi-function support
- Strategy: Sequential Merge (Option A) - merge all functions in call order
- Effort estimate: 5.5-7.5 hours
- Deliverables: README.md (16KB), current-analysis.md (15KB), QUICKSTART.md (5.8KB)

Files Modified/Created:
- src/mir/loop_pattern_detection.rs (+50 lines) - Pattern detection
- src/mir/join_ir/lowering/simple_while_minimal.rs (+219 lines) - Lowering
- src/mir/join_ir/lowering/loop_patterns.rs (+803 lines) - Foundation skeleton
- src/mir/join_ir/lowering/mod.rs (+2 lines) - Module registration
- src/mir/builder/control_flow.rs (+1 line) - Routing fix
- src/mir/builder/loop_frontend_binding.rs (+20 lines) - Binding updates
- tools/test_phase188_foundation.sh (executable) - Foundation verification
- CURRENT_TASK.md (updated) - Phase 188/189 status

Next: Phase 189 implementation (merge_joinir_mir_blocks refactor)

🤖 Generated with Claude Code

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

src/mir/join_ir/lowering/simple_while.rs

@@ -0,0 +1,107 @@
+//! Pattern 1: Simple While Loop → JoinIR Lowering
+//!
+//! Phase 188 Task 188-4: Implementation of simple while loop pattern.
+//!
+//! ## Pattern Characteristics
+//!
+//! - Single loop variable (carrier)
+//! - Simple condition
+//! - NO control flow statements (no break, no continue, no nested if)
+//! - Natural exit only (condition becomes false)
+//!
+//! ## Example
+//!
+//! ```nyash
+//! local i = 0
+//! loop(i < 3) {
+//!   print(i)
+//!   i = i + 1
+//! }
+//! return 0
+//! ```
+//!
+//! ## JoinIR Transformation
+//!
+//! ```text
+//! fn main():
+//!   i_init = 0
+//!   return loop_step(i_init)
+//!
+//! fn loop_step(i):
+//!   exit_cond = !(i < 3)
+//!   Jump(k_exit, [], cond=exit_cond)  // early return
+//!   print(i)
+//!   i_next = i + 1
+//!   Call(loop_step, [i_next])  // tail recursion
+//!
+//! fn k_exit():
+//!   return 0
+//! ```
+
+use crate::mir::join_ir::lowering::loop_scope_shape::LoopScopeShape;
+use crate::mir::join_ir::{
+    ConstValue, JoinContId, JoinFuncId, JoinFunction, JoinInst, JoinModule, MirLikeInst, UnaryOp,
+};
+use crate::mir::ValueId;
+
+/// Pattern detection: Simple While Loop
+///
+/// Criteria:
+/// - No break statements (break_targets.is_empty())
+/// - No continue statements (continue_targets.is_empty())
+/// - Has at least one carrier variable
+///
+/// # Returns
+///
+/// - `true`: Pattern matches (safe to call lower_simple_while_pattern)
+/// - `false`: Pattern does not match (try other patterns)
+pub fn is_simple_while_pattern(_scope: &LoopScopeShape) -> bool {
+    // Phase 188: Pattern detection logic will be implemented after understanding
+    // LoopScopeShape structure better. For now, return false to avoid breaking existing code.
+    // TODO: Implement proper detection based on break_targets, continue_targets, and carriers.
+    false
+}
+
+/// Lower simple while loop to JoinIR
+///
+/// Transforms a simple while loop (Pattern 1) into JoinIR representation:
+/// - Loop → tail-recursive function (loop_step)
+/// - Exit condition → conditional Jump to k_exit
+/// - Loop body → sequential Compute instructions
+/// - Backedge → tail Call to loop_step
+///
+/// # Arguments
+///
+/// - `scope`: LoopScopeShape containing loop structure and variable classification
+///
+/// # Returns
+///
+/// - `Some(JoinModule)`: Successfully lowered to JoinIR
+/// - `None`: Lowering failed (try other patterns or fallback)
+pub fn lower_simple_while_pattern(_scope: LoopScopeShape) -> Option<JoinModule> {
+    // Phase 188: Lowering implementation
+    // This is a skeleton that will be filled in after examining LoopScopeShape structure
+    // and understanding how to extract loop header, body, latch, and exit information.
+
+    // TODO Phase 188-4:
+    // 1. Extract carrier variables from scope.carriers
+    // 2. Create JoinModule with 3 functions: main/entry, loop_step, k_exit
+    // 3. Generate exit condition check (negate loop condition)
+    // 4. Generate conditional Jump to k_exit
+    // 5. Generate loop body instructions
+    // 6. Generate tail Call to loop_step with updated carriers
+    // 7. Wire k_exit to return appropriate value
+
+    None // Placeholder
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_pattern_detection_placeholder() {
+        // Placeholder test - will be implemented with actual LoopScopeShape instances
+        // after understanding the structure better
+    }
+}