fix(ego-field-test): indent multi-line expressions in json_extract wrapper

The json_extract helper (introduced in 685d3dc) wraps Python expressions
in try/except but relied on template whitespace to indent the first line.
Multi-line expressions had subsequent lines at column 0, outside the try
block, causing IndentationError for all but the first few extensions.

Pipe expressions through sed to indent every line by 4 spaces.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: ZviBaratz

scripts/field-test-runner.sh

@@ -34,10 +34,12 @@ HISTORY_FILE="$ROOT_DIR/field-tests/history.jsonl"
 json_extract() {
     local context="$1"; shift
     local expr="$1"; shift
+    local indented
+    indented="$(printf '%s\n' "$expr" | sed '/^[[:space:]]*$/d' | sed 's/^/    /')"
     python3 -c "
 import json, sys
 try:
-    $expr
+$indented
 except (json.JSONDecodeError, KeyError, IndexError, TypeError) as e:
     print(f'Error ($context): {type(e).__name__}: {e}', file=sys.stderr)
     sys.exit(1)