phase29ab(p2): add seg trim fixture+smoke and docs

apps/tests/phase29ab_pattern2_loopbodylocal_seg_min.hako

@@ -0,0 +1,28 @@
+// Phase 29ab P2: Pattern2 LoopBodyLocal Trim (seg) minimal case
+//
+// Goal:
+// - break condition uses LoopBodyLocal (seg) with Trim A-3 shape
+// - JoinIR -> merge path should handle promotion
+//
+// Expected (before fix): FAIL/out-of-scope
+// Expected (after fix): prints "2" and returns 2
+
+static box Main {
+    main() {
+        local s = "ab "
+        local i = 0
+
+        loop(i < s.length()) {
+            local seg = s.substring(i, i + 1)
+
+            if seg == " " || seg == "\t" {
+                break
+            }
+
+            i = i + 1
+        }
+
+        print(i)
+        return i
+    }
+}

src/mir/builder/control_flow/joinir/patterns/pattern2/README.md

@@ -10,6 +10,11 @@
 - Supported: A-3 Trim / A-4 DigitPos (promote LoopBodyLocal to carrier)
 - ConditionOnly carriers are recalculated per iteration (no host binding)
 
+## Trim (seg) minimal shape
+- Example shape (A-3): `local seg = s.substring(i, i + 1)`
+- Break guard: `if seg == " " || seg == "\\t" { break }`
+- seg is read-only (no reassignment in the loop body)
+
 ## Carrier binding rules (Pattern2)
 - `CarrierInit::FromHost` -> host binding required
 - `CarrierInit::BoolConst(_)` / `CarrierInit::LoopLocalZero` -> host binding is skipped
@@ -19,6 +24,7 @@
 - multiple breaks / continue / return in the loop body
 - reassigned LoopBodyLocal or ReadOnlySlot contract violations
 - break conditions with unsupported AST shapes
+- seg reassignment or non-substring init (e.g., `seg = other_call()`)
 
 ## Fail-Fast policy
 - `PromoteDecision::Freeze` -> Err (missing implementation or contract violation)

tools/smokes/v2/profiles/integration/apps/phase29ab_pattern2_loopbodylocal_seg_min_vm.sh

@@ -0,0 +1,34 @@
+#!/bin/bash
+# Phase 29ab P2: Pattern2 LoopBodyLocal Trim (seg) minimal (VM backend)
+# Tests: LoopBodyLocal seg in break condition promoted via Trim A-3
+
+source "$(dirname "$0")/../../../lib/test_runner.sh"
+export SMOKES_USE_PYVM=0
+require_env || exit 2
+
+INPUT="$NYASH_ROOT/apps/tests/phase29ab_pattern2_loopbodylocal_seg_min.hako"
+RUN_TIMEOUT_SECS=${RUN_TIMEOUT_SECS:-10}
+
+set +e
+OUTPUT=$(timeout "$RUN_TIMEOUT_SECS" env NYASH_DISABLE_PLUGINS=1 HAKO_JOINIR_STRICT=1 "$NYASH_BIN" "$INPUT" 2>&1)
+EXIT_CODE=$?
+set -e
+
+if [ "$EXIT_CODE" -eq 124 ]; then
+    test_fail "phase29ab_pattern2_loopbodylocal_seg_min_vm: hakorune timed out (>${RUN_TIMEOUT_SECS}s)"
+    exit 1
+fi
+
+OUTPUT_CLEAN=$(echo "$OUTPUT" | filter_noise)
+
+if echo "$OUTPUT_CLEAN" | grep -q "^2$" || echo "$OUTPUT" | grep -q "^RC: 2$"; then
+    test_pass "phase29ab_pattern2_loopbodylocal_seg_min_vm: Pattern2 Trim promotion succeeded (output: 2)"
+    exit 0
+else
+    echo "[FAIL] Unexpected output (expected: 2)"
+    echo "[INFO] Exit code: $EXIT_CODE"
+    echo "[INFO] Output (clean):"
+    echo "$OUTPUT_CLEAN" | tail -n 20 || true
+    test_fail "phase29ab_pattern2_loopbodylocal_seg_min_vm: Unexpected output"
+    exit 1
+fi