test(redirect): add append redirect spec tests

crates/bashkit/tests/spec_cases/bash/append_redirect.test.sh

@@ -0,0 +1,74 @@
+# Append redirect tests
+# Tests that >> does not duplicate content in compound commands (issue #1119)
+
+### append_simple
+# Simple append works
+echo "line1" > /tmp/append.txt
+echo "line2" >> /tmp/append.txt
+cat /tmp/append.txt
+### expect
+line1
+line2
+### end
+
+### append_brace_group
+# Brace group append writes once
+rm -f /tmp/brace.txt
+{ echo "line1"; echo "line2"; } >> /tmp/brace.txt
+cat /tmp/brace.txt
+### expect
+line1
+line2
+### end
+
+### append_brace_group_existing_file
+# Brace group append to existing file
+echo "existing" > /tmp/exist.txt
+{ echo "new1"; echo "new2"; } >> /tmp/exist.txt
+cat /tmp/exist.txt
+### expect
+existing
+new1
+new2
+### end
+
+### append_no_duplicate
+# Repeated appends should not duplicate
+rm -f /tmp/nodup.txt
+echo "first" >> /tmp/nodup.txt
+echo "second" >> /tmp/nodup.txt
+cat /tmp/nodup.txt
+### expect
+first
+second
+### end
+
+### append_if_else
+# if/else with append redirect
+rm -f /tmp/ifelse.txt
+if false; then
+    echo "yes"
+else
+    echo "no"
+fi >> /tmp/ifelse.txt
+cat /tmp/ifelse.txt
+### expect
+no
+### end
+
+### append_rebuild_cycle
+# Simulate bashblog rebuild: create file, then append-only should not duplicate
+rm -f /tmp/footer.html
+{
+    echo "<div>footer line 1</div>"
+    echo "<div>footer line 2</div>"
+} >> /tmp/footer.html
+# Rebuild: run the same block again — should append, not duplicate first block
+{
+    echo "<div>footer line 1</div>"
+    echo "<div>footer line 2</div>"
+} >> /tmp/footer.html
+wc -l < /tmp/footer.html
+### expect
+4
+### end