test: Phase 100 string accumulator fixture+smokes (VM+LLVM)

- Add phase100_string_accumulator_min.hako fixture
  * out = out + ch string accumulation
  * print(out.length()) for stable numeric output
- Add VM smoke: phase100_string_accumulator_vm.sh
- Add LLVM EXE smoke: phase100_string_accumulator_llvm_exe.sh (Phase 97 gating)
- Regression: all phase100/97/94 tests pass

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

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

apps/tests/phase100_string_accumulator_min.hako

@@ -0,0 +1,15 @@
+static box Main {
+    main() {
+        local out = ""
+        local s = "abc"
+        local i = 0
+        loop(i < 3) {
+            if i >= 3 { break }
+            local ch = s.substring(i, i + 1)
+            out = out + ch
+            i = i + 1
+        }
+        print(out.length())
+        return 0
+    }
+}

tools/smokes/v2/profiles/integration/apps/phase100_string_accumulator_llvm_exe.sh

@@ -0,0 +1,49 @@
+#!/bin/bash
+# Phase 100 P3 - String Accumulator (LLVM EXE backend)
+
+set -e
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+REPO_ROOT="$(cd "$SCRIPT_DIR/../../../../../.." && pwd)"
+
+cd "$REPO_ROOT"
+
+HAKO_FILE="apps/tests/phase100_string_accumulator_min.hako"
+EXPECTED_OUTPUT="3"
+
+# Phase 97 plugin gating pattern
+if [ ! -f "target/release/plugins/.dlopen_cache" ]; then
+    echo "⏭️  SKIP: phase100_string_accumulator_llvm_exe (plugins not built)"
+    exit 0
+fi
+
+# Build LLVM exe
+if ! tools/build_llvm.sh "$HAKO_FILE" > /tmp/phase100_string_acc_build.log 2>&1; then
+    echo "⚠️  SKIP: phase100_string_accumulator_llvm_exe (LLVM build failed)"
+    cat /tmp/phase100_string_acc_build.log | tail -n 20
+    exit 0
+fi
+
+EXE_PATH="/tmp/phase100_string_accumulator_min"
+
+if [ ! -f "$EXE_PATH" ]; then
+    echo "❌ FAIL: phase100_string_accumulator_llvm_exe (exe not found)"
+    exit 1
+fi
+
+# Run exe and extract numeric output
+ACTUAL_OUTPUT=$("$EXE_PATH" 2>&1 | grep -v '^\[' | grep -v 'Net plugin' | grep -v 'RC:' | grep -E '^[0-9]+$')
+
+if [ "$ACTUAL_OUTPUT" = "$EXPECTED_OUTPUT" ]; then
+    echo "✅ PASS: phase100_string_accumulator_llvm_exe"
+    exit 0
+else
+    echo "❌ FAIL: phase100_string_accumulator_llvm_exe"
+    echo "Expected:"
+    echo "$EXPECTED_OUTPUT"
+    echo "Got:"
+    echo "$ACTUAL_OUTPUT"
+    echo "---Full output (last 80 lines):---"
+    "$EXE_PATH" 2>&1 | tail -n 80
+    exit 1
+fi

tools/smokes/v2/profiles/integration/apps/phase100_string_accumulator_vm.sh

@@ -0,0 +1,22 @@
+#!/bin/bash
+# Phase 100 P3 - String Accumulator (VM backend)
+
+HAKO_FILE="apps/tests/phase100_string_accumulator_min.hako"
+BACKEND="vm"
+EXPECTED_OUTPUT="3"
+
+ACTUAL_OUTPUT=$(HAKO_JOINIR_STRICT=1 ./target/release/hakorune --backend "$BACKEND" "$HAKO_FILE" 2>&1 | grep -v '^\[' | grep -v 'Net plugin' | grep -v 'RC:' | grep -E '^[0-9]+$')
+
+if [ "$ACTUAL_OUTPUT" = "$EXPECTED_OUTPUT" ]; then
+    echo "✅ PASS: phase100_string_accumulator_vm"
+    exit 0
+else
+    echo "❌ FAIL: phase100_string_accumulator_vm"
+    echo "Expected:"
+    echo "$EXPECTED_OUTPUT"
+    echo "Got:"
+    echo "$ACTUAL_OUTPUT"
+    echo "---Full output (last 80 lines):---"
+    HAKO_JOINIR_STRICT=1 ./target/release/hakorune --backend "$BACKEND" "$HAKO_FILE" 2>&1 | tail -n 80
+    exit 1
+fi