Looked at the diff. The apply_payload_limits refactor and the test changes are fine. Three things to fix:

1. (blocking) local_mode is missing in the async client - async_client.py log() only checks self._closed, so with AsyncLogTideClient and local_mode=True logs still get sent. And since local_mode=True allows api_key=None, the async client will attempt to send with a null key. The same guard from the sync client needs to be replicated:

if self._closed or self.options.local_mode is True:
    return
if self.options.local_mode == "if_unset_api_key" and not self.options.api_key:
    return

2. dsn now always overwrites explicit api_url/api_key (models.py __post_init__). Before, explicit values won (if not self.api_url: ...); now dsn always wins and hand-passed values are silently dropped. Intentional?

3. default api_url = production + relaxed validation (models.py). With api_url now defaulting to https://api.logtide.dev, building ClientOptions(api_key="...") without a url or dsn no longer raises and silently points at prod. It used to raise ValueError. A misconfig ends up in production unnoticed.

Minor: dead comment # if self.options and the two TODOs in log(), plus a typo in the error message ("other then" -> "other than").

Re-checked after the refactor. The three original points are resolved: async now honors local_mode via BaseClient._is_logging_disabled(), the dsn-overwrites-explicit behavior is gone, and api_url no longer defaults to production. Nice.

Remaining changes requested:

1. Keep dsn as an option instead of the from_dsn factory. The other SDKs expose dsn as a first-class option, so the Python SDK should match for parity. Concretely:

• restore dsn: str | None = None as a field
• api_url back to str | None = None (not a required positional)
• in __post_init__, if dsn is set, parse it and fill api_url/api_key. Pick a precedence and document it (dsn wins, or self.api_url = self.api_url or parts.api_url if explicit should win)
• validation: with local_mode off, require dsn or (api_url + api_key)
• drop from_dsn once dsn is a field. This also removes the mutable default global_metadata={} and the ~18-field duplication in its signature.

2. Initialize self._trace_id in BaseClient.__init__. Right now the base class reads self._trace_id (in get_trace_id / _pin_trace_id_to_entry) but only the subclasses set it. A subclass that forgets it crashes with AttributeError. Set it to None in the base.

3. Restore the metadata None coercion. The old if entry.metadata is None: entry.metadata = {} was dropped, so client.log(LogEntry(..., metadata=None)) now crashes on {**entry.metadata}. Minor, but it used to be handled.

Nits: redundant validation (BaseClient.__init__ raises RuntimeError for the missing-key case that ClientOptions.__post_init__ already rejects), and typo in the error message: "other then" -> "other than".

local_mode itself is good, leave it as is.