fix(js): convert PolyglotException to JsEvaluationException at the engine boundary

[amanjeetsingh150]

Summary

GraalJsEngine now catches PolyglotException at every context.eval() call site (the IIFE evaluation path and the bootstrap script) and rethrows a plain JsEvaluationException(JsScriptError). Live polyglot internals never escape the engine.

Why

PolyglotException exposes a polyglotStackTrace: List<StackFrame> property whose getLanguage() callback re-enters the originating PolyglotContext. If a caller retains the exception on a model that's later walked by a reflective serializer (Jackson and friends) after the engine has closed, that callback hits ShouldNotReachHere and the JVM dies.

Stripping the exception to plain Strings at the boundary is a one-place fix that closes this class of failure for every downstream consumer of JsEngine.evaluateScript — without anyone having to remember to do safe-extraction at every call site.

Shape of the new types

data class JsScriptError(
    val message: String,
    val causeMessage: String?,
    val sourceClass: String,
    val stackFrames: List<String>,   // formatted, not live frames
    val isHostException: Boolean,
    val isGuestException: Boolean,
)

class JsEvaluationException(val error: JsScriptError) : RuntimeException(error.message)

Resolved entirely while the engine is still open. After the constructor returns, the original PolyglotException can be released and the engine closed without affecting the wrapper.

Behaviour change for library users

Callers that previously caught PolyglotException from JsEngine.evaluateScript now catch JsEvaluationException. Broad catches (Throwable / Exception) are unaffected — the exception still propagates as a RuntimeException. The CLI's own error formatter (ErrorViewUtils) is not impacted; it falls through to e.stackTraceToString() either way.

Migration

// before
} catch (e: PolyglotException) { ... }

// after
} catch (e: JsEvaluationException) {
    // e.message — the JS error message
    // e.error.causeMessage — host cause message, if any
    // e.error.stackFrames — formatted strings, no live frames
}

Verify

• ./gradlew test passes across all modules.
• New tests in GraalJsEngineTest cover the wrapping behaviour, JsScriptError shape, and Jackson round-trip with the engine closed.
• Existing sandboxing works test updated to expect the new exception type.