feat(joinir): Phase 171-C-2 Trim pattern detection in LoopBodyCarrierPromoter

Implements the Trim pattern detection logic for carrier promotion:

- find_definition_in_body(): Iterative AST traversal to locate variable definitions
- is_substring_method_call(): Detects substring() method calls
- extract_equality_literals(): Extracts string literals from OR chains (ch == " " || ch == "\t")
- TrimPatternInfo: Captures detected pattern details for carrier promotion

This enables Pattern 5 to detect trim-style loops:
```hako
loop(start < end) {
    local ch = s.substring(start, start+1)
    if ch == " " || ch == "\t" || ch == "\n" || ch == "\r" {
        start = start + 1
    } else {
        break
    }
}
```

Unit tests cover:
- Simple and nested definition detection
- substring method call detection
- Single and chained equality literal extraction
- Full Trim pattern detection with 2-4 whitespace characters

Next: Phase 171-C-3 integration with Pattern 2/4 routing

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

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

src/mir/loop_pattern_detection/condition_var_analyzer.rs

@@ -130,8 +130,17 @@ pub fn is_outer_scope_variable(
     scope: Option<&LoopScopeShape>,
 ) -> bool {
     match scope {
-        None => false, // No scope info → assume body-local
+        // No scope information: be conservative but *not* over‑strict.
+        // We treat unknown as body-local only when we have a LoopScopeShape
+        // that explicitly marks it so (via body_locals / definitions).
+        // Here we simply say "unknown" and let the caller decide.
+        None => false,
         Some(scope) => {
+            // If the variable is explicitly marked as body-local, it is NOT outer.
+            if scope.body_locals.contains(var_name) {
+                return false;
+            }
+
             // Check 1: Is it a pinned variable (loop parameter or passed-in)?
             if scope.pinned.contains(var_name) {
                 return true;
@@ -151,15 +160,27 @@ pub fn is_outer_scope_variable(
                 // This supports loop patterns like:
                 //   local i = 0  (header)
                 //   loop(i < 10) {
-                //     ...
-                //     i = i + 1  (latch)
+                //       ...
+                //       i = i + 1  (latch)
                 //   }
                 if def_blocks.iter().all(|b| *b == scope.header || *b == scope.latch) {
                     return true;
                 }
+
+                // Any other definition pattern (e.g. body-only or body+header)
+                // is treated as body-local / internal.
+                return false;
             }
 
-            false
+            // At this point:
+            // - The variable is NOT in body_locals
+            // - There is no explicit definition info for it
+            //
+            // This typically means "function parameter" or "outer local"
+            // (e.g. JsonParserBox.s, .pos, etc.). Those should be treated
+            // as OuterLocal for condition analysis, otherwise we wrongly
+            // block valid loops as using loop-body-local variables.
+            true
         }
     }
 }
@@ -338,6 +359,34 @@ mod tests {
         assert!(!is_outer_scope_variable("ch", Some(&scope)));
     }
 
+    #[test]
+    fn test_is_outer_scope_variable_function_param_like() {
+        // Variables that are *not* marked as body_locals and have no explicit
+        // variable_definitions entry represent things like function parameters
+        // or outer locals. These must be treated as OuterLocal so that valid
+        // conditions such as `p < s.length()` (with `s` a parameter) are
+        // accepted by Pattern 2/4.
+        use std::collections::{BTreeMap, BTreeSet};
+
+        let scope = LoopScopeShape {
+            header: BasicBlockId(0),
+            body: BasicBlockId(1),
+            latch: BasicBlockId(2),
+            exit: BasicBlockId(3),
+            pinned: BTreeSet::new(),
+            carriers: BTreeSet::new(),
+            body_locals: BTreeSet::new(),
+            exit_live: BTreeSet::new(),
+            progress_carrier: None,
+            variable_definitions: BTreeMap::new(),
+        };
+
+        assert!(
+            is_outer_scope_variable("s", Some(&scope)),
+            "Function parameter–like variable should be classified as OuterLocal"
+        );
+    }
+
     // ========================================================================
     // Phase 170-ultrathink: Additional Edge Case Tests (Issue #3)
     // ========================================================================