[chalmerlowe]

Summary

Stacked on #18868.

Populates client_options.api_endpoint with the transport's resolved self._host in Transport.__init__ (base.py.j2) when client_options is provided without an explicit api_endpoint override.

Why

• Previously, _extract_endpoint_attributes in google-api-core only populated server.address and non-default server.port on Tier 3 (GAPIC client) and gRPC Tier 4 (wire attempt) spans when the caller explicitly passed ClientOptions(api_endpoint=...).
• When a client or transport connected using the service's DEFAULT_HOST (or a host passed directly to the transport constructor) without setting client_options.api_endpoint, server.address and server.port were omitted from Tier 3 and gRPC Tier 4 spans.
• Defaulting client_options.api_endpoint to self._host in the base transport constructor ensures Tier 3 and gRPC Tier 4 spans consistently record server.address and non-default server.port.

Files Modified

• packages/gapic-generator/gapic/templates/%namespace/%name_%version/%sub/services/%service/transports/base.py.j2
• packages/gapic-generator/gapic/templates/tests/unit/gapic/%name_%version/%sub/test_%service.py.j2
• packages/gapic-generator/tests/system/telemetry_requirements_matrix.csv
• packages/gapic-generator/tests/integration/goldens/**

[gemini-code-assist]

Code Review

This pull request updates the base transport templates and generated golden files to automatically populate the api_endpoint in client_options with the transport's host if it is not already set, supporting both ClientOptions instances and dictionaries. It also updates the corresponding unit tests and telemetry requirements matrix. A review comment correctly points out that mutating client_options in-place can cause unexpected side effects if the caller reuses the options object, and suggests copying the options before modification.

[gemini-code-assist]

Mutating the client_options argument in-place (whether it is a ClientOptions instance or a dict) can lead to unexpected side effects if the caller reuses the same options object across multiple client or transport instances. To prevent this, we should create a copy of the options before modifying them.

        if isinstance(client_options, client_options_lib.ClientOptions):
            if not client_options.api_endpoint:
                import copy
                client_options = copy.copy(client_options)
                client_options.api_endpoint = self._host
        elif isinstance(client_options, dict):
            if not client_options.get("api_endpoint"):
                client_options = dict(client_options)
                client_options["api_endpoint"] = self._host