feat(joinir): Phase 223.5 - LoopBodyCondPromoter Pattern2 integration

- Integrate LoopBodyCondPromoter into Pattern2 (break condition analysis)
- Add Pattern2 error message functions to error_messages.rs
- Create A-4 minimal test (phase2235_p2_digit_pos_min.hako)
- Unified promotion structure for Pattern2/Pattern4

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/mir/loop_pattern_detection/error_messages.rs

@@ -95,3 +95,210 @@ mod tests {
         assert!(err.contains("Pattern 4 supports"));
     }
 }
+
+// ========================================================================
+// Pattern 4 Specific Error Messages
+// ========================================================================
+
+/// Pattern4: Cannot promote LoopBodyLocal variables in condition
+///
+/// Used when LoopBodyCondPromoter fails to promote a LoopBodyLocal variable
+/// used in loop conditions to a bool carrier.
+///
+/// # Arguments
+///
+/// * `vars` - Names of LoopBodyLocal variables that failed promotion
+/// * `reason` - Human-readable reason for the failure
+///
+/// # Example
+///
+/// ```
+/// let err = format_error_pattern4_promotion_failed(&["ch"], "not a Trim pattern");
+/// // Returns: "[cf_loop/pattern4] Cannot promote LoopBodyLocal variables ["ch"]: not a Trim pattern"
+/// ```
+pub fn format_error_pattern4_promotion_failed(vars: &[String], reason: &str) -> String {
+    format!(
+        "[cf_loop/pattern4] Cannot promote LoopBodyLocal variables {:?}: {}",
+        vars, reason
+    )
+}
+
+/// Pattern4: Trim pattern detected but not safe
+///
+/// Used when a Trim pattern is detected but does not meet safety criteria
+/// (e.g., too many whitespace characters, unsafe structure).
+///
+/// # Arguments
+///
+/// * `carrier_name` - Name of the carrier variable
+/// * `whitespace_count` - Number of whitespace characters detected
+///
+/// # Example
+///
+/// ```
+/// let err = format_error_pattern4_trim_not_safe("is_whitespace", 5);
+/// // Returns: "[cf_loop/pattern4] Trim pattern detected but not safe: carrier='is_whitespace', whitespace_count=5"
+/// ```
+pub fn format_error_pattern4_trim_not_safe(carrier_name: &str, whitespace_count: usize) -> String {
+    format!(
+        "[cf_loop/pattern4] Trim pattern detected but not safe: carrier='{}', whitespace_count={}",
+        carrier_name, whitespace_count
+    )
+}
+
+/// Pattern4: Lowering failed
+///
+/// Generic error wrapper for Pattern 4 lowering failures.
+///
+/// # Arguments
+///
+/// * `cause` - The underlying error message
+///
+/// # Example
+///
+/// ```
+/// let err = format_error_pattern4_lowering_failed("JoinIR conversion error");
+/// // Returns: "[cf_loop/pattern4] Lowering failed: JoinIR conversion error"
+/// ```
+pub fn format_error_pattern4_lowering_failed(cause: &str) -> String {
+    format!("[cf_loop/pattern4] Lowering failed: {}", cause)
+}
+
+/// Pattern4: Carrier not found in variable_map
+///
+/// Used when an expected carrier variable is missing from variable_map,
+/// indicating an exit binding is not properly generated.
+///
+/// # Arguments
+///
+/// * `carrier_name` - Name of the missing carrier variable
+///
+/// # Example
+///
+/// ```
+/// let err = format_error_pattern4_carrier_not_found("sum");
+/// // Returns: "[cf_loop/pattern4] Carrier 'sum' not found in variable_map - exit binding missing"
+/// ```
+pub fn format_error_pattern4_carrier_not_found(carrier_name: &str) -> String {
+    format!(
+        "[cf_loop/pattern4] Carrier '{}' not found in variable_map - exit binding missing",
+        carrier_name
+    )
+}
+
+// ========================================================================
+// Pattern 2 Specific Error Messages
+// ========================================================================
+
+/// Pattern2: Cannot promote LoopBodyLocal variables in condition
+///
+/// Used when LoopBodyCondPromoter fails to promote a LoopBodyLocal variable
+/// used in loop/break conditions to a bool carrier.
+///
+/// # Arguments
+///
+/// * `vars` - Names of LoopBodyLocal variables that failed promotion
+/// * `reason` - Human-readable reason for the failure
+///
+/// # Example
+///
+/// ```
+/// let err = format_error_pattern2_promotion_failed(&["ch"], "not a Trim pattern");
+/// // Returns: "[cf_loop/pattern2] Cannot promote LoopBodyLocal variables ["ch"]: not a Trim pattern"
+/// ```
+pub fn format_error_pattern2_promotion_failed(vars: &[String], reason: &str) -> String {
+    format!(
+        "[cf_loop/pattern2] Cannot promote LoopBodyLocal variables {:?}: {}",
+        vars, reason
+    )
+}
+
+/// Pattern2: Trim pattern detected but not safe
+///
+/// Used when a Trim pattern is detected but does not meet safety criteria.
+///
+/// # Arguments
+///
+/// * `carrier_name` - Name of the carrier variable
+/// * `whitespace_count` - Number of whitespace characters detected
+pub fn format_error_pattern2_trim_not_safe(carrier_name: &str, whitespace_count: usize) -> String {
+    format!(
+        "[cf_loop/pattern2] Trim pattern detected but not safe: carrier='{}', whitespace_count={}",
+        carrier_name, whitespace_count
+    )
+}
+
+#[cfg(test)]
+mod pattern2_tests {
+    use super::*;
+
+    #[test]
+    fn test_format_error_pattern2_promotion_failed() {
+        let vars = vec!["ch".to_string(), "digit_pos".to_string()];
+        let err = format_error_pattern2_promotion_failed(&vars, "cascading LoopBodyLocal");
+
+        assert!(err.contains("[cf_loop/pattern2]"));
+        assert!(err.contains("Cannot promote"));
+        assert!(err.contains("ch"));
+        assert!(err.contains("digit_pos"));
+        assert!(err.contains("cascading LoopBodyLocal"));
+    }
+
+    #[test]
+    fn test_format_error_pattern2_trim_not_safe() {
+        let err = format_error_pattern2_trim_not_safe("is_digit", 3);
+
+        assert!(err.contains("[cf_loop/pattern2]"));
+        assert!(err.contains("Trim pattern"));
+        assert!(err.contains("not safe"));
+        assert!(err.contains("is_digit"));
+        assert!(err.contains("whitespace_count=3"));
+    }
+}
+
+#[cfg(test)]
+mod pattern4_tests {
+    use super::*;
+
+    #[test]
+    fn test_format_error_pattern4_promotion_failed() {
+        let vars = vec!["ch".to_string(), "temp".to_string()];
+        let err = format_error_pattern4_promotion_failed(&vars, "not a Trim pattern");
+
+        assert!(err.contains("[cf_loop/pattern4]"));
+        assert!(err.contains("Cannot promote"));
+        assert!(err.contains("ch"));
+        assert!(err.contains("temp"));
+        assert!(err.contains("not a Trim pattern"));
+    }
+
+    #[test]
+    fn test_format_error_pattern4_trim_not_safe() {
+        let err = format_error_pattern4_trim_not_safe("is_whitespace", 5);
+
+        assert!(err.contains("[cf_loop/pattern4]"));
+        assert!(err.contains("Trim pattern"));
+        assert!(err.contains("not safe"));
+        assert!(err.contains("is_whitespace"));
+        assert!(err.contains("whitespace_count=5"));
+    }
+
+    #[test]
+    fn test_format_error_pattern4_lowering_failed() {
+        let err = format_error_pattern4_lowering_failed("JoinIR error");
+
+        assert!(err.contains("[cf_loop/pattern4]"));
+        assert!(err.contains("Lowering failed"));
+        assert!(err.contains("JoinIR error"));
+    }
+
+    #[test]
+    fn test_format_error_pattern4_carrier_not_found() {
+        let err = format_error_pattern4_carrier_not_found("sum");
+
+        assert!(err.contains("[cf_loop/pattern4]"));
+        assert!(err.contains("Carrier 'sum'"));
+        assert!(err.contains("not found"));
+        assert!(err.contains("exit binding missing"));
+    }
+}