prop.setExpression keeps an expression with a syntax error but disables
it, and says why only in its own reply. MCP set_property answers with
prop.get instead, and prop.get reported `evaluated` / `expressionError`
only for enabled expressions, so set_property, get_property and prop.get
all showed the broken expression as if it were installed.
prop.get now reports a disabled expression too: `evaluated` is the
static value that renders, and `expressionError` is its syntax error.
Test: expression_syntax_errors_reach_the_reply (set_property and
get_property carry the SyntaxError; runtime errors and valid expressions
report as before).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>