fix: propagate native error message instead of discarding it

[guidofawkes328]

Problem

On Android, create() / get() reject with the coarse mapped error code as both the code and the message:

promise.reject(errorCode, errorCode)

This discards the real CreateCredentialException.errorMessage (e.g. "RP ID cannot be validated."). The JS wrapper (handleNativeError) then maps the code to a hardcoded generic string, so callers only ever see something like "The request failed. No Credentials were returned." — misleading, and useless for diagnosing configuration problems (RP ID / assetlinks mismatches, etc.).

Several distinct DOM errors (NotAllowedError, DataError = "RP ID cannot be validated", SecurityError) all collapse to RequestFailed, so the code alone cannot tell them apart — the message is the only signal, and it was being thrown away.

There was also no fallback catch around the coroutine body, so a non-CredentialException failure could leave the promise unsettled (a hang).

Fix

Non-breaking — error codes are unchanged, so programmatic .error === 'RequestFailed' checks keep working. Only the message now carries the native detail.

• Android (PasskeyModule.kt): reject with the native message while keeping the code:

  promise.reject(errorCode, e.errorMessage?.toString() ?: errorCode)

  for both create() and get(), plus a catch (e: Throwable) fallback so unexpected failures reject with detail instead of hanging.
• iOS (Passkey.swift): the primary error path already propagated error.localizedDescription. Aligned the get() decode-catch with create() so it rejects with a mapped code + localizedDescription instead of the verbose debugDescription for both fields.
• JS (PasskeyError.ts): prefer the native message over the generic per-code fallback when it carries additional detail; fall back to the existing generic message otherwise. Added message?: string to TNativeError.

Before / After

Given a native failure with errorMessage = "RP ID cannot be validated.":

• Before: { error: 'RequestFailed', message: 'The request failed. No Credentials were returned.' }
• After: { error: 'RequestFailed', message: 'RP ID cannot be validated.' }

Verification

yarn tsc --noEmit, eslint, and the Jest suite all pass. Kotlin/Swift were not compiled in isolation but the edits are syntactically consistent with the surrounding code and existing imports.

Related

• Fixes Error: [50152] RP ID cannot be validated on Android #68 ("[50152] RP ID cannot be validated on Android") — the underlying message is now surfaced to callers.
• Related to error-normalization discussion in Android: Pressing Back during Passkey.get() returns RequestFailed instead of UserCancelled #106 / fix: normalize cancellation / no-credential errors on Android & iOS (#106, #107) #108 — this keeps the normalized codes but stops discarding the native detail.