Gemini needs none of the machinery Bedrock needed. litellm composes
{api_base}/models/{model}:{endpoint} from a custom api_base, so a plain
path-prefixed mount reaches it, and the credential travels as a static
x-goog-api-key header that no host rewrite invalidates. Nothing is
re-signed and nothing leaves the cache key, so a recording still cannot
cross credentials.
A finished turn names a finishReason on every candidate and reports
usageMetadata. The reason is read as a string rather than compared to
STOP: MAX_TOKENS and the safety reasons end a turn just as finally, and
rejecting them would send every one of them upstream forever. Streaming
is the half worth care. Gemini repeats usageMetadata on every chunk and
names a finishReason only on the last, so the terminator is the final
event rather than any event, and a stream the connection cut short ends
on a chunk carrying usage and no reason.
The mount's upstream base carries the API version, so the path the rules
see is /v1beta/models/..., not the one the proxy sent. The first version
of this anchored the rule at the start of that path, which passed every
test against a stub with no version prefix and would have cached nothing
at all in a real run. Caught by replaying the rules over responses
captured from live gemini-2.5-flash, which is also why the tests now
mount their stub under the version prefix.
Vertex stays unmounted and is a separate provider here: litellm grafts
the default Vertex path onto an api_base only when that api_base has no
path of its own, so Vertex needs a root-mounted edge on its own port.
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