Built-in providers that speak the OpenAI Chat wire format skipped
normalizeOpenAICompatibleTools(), which only ran for custom
openai-compatible-* connections. A client tool whose type is not
"function" (a named Claude server tool, a nameless hosted tool) was
forwarded verbatim, and agentrouter's GLM backend rejected the whole
request with 400 tools[0].type:type is illegal.
Extract the gate into shouldNormalizeFunctionToolsOnly(): custom
openai-compatible-* providers keep normalizing on every target, and a
conservative allowlist of built-in providers (agentrouter first)
normalizes on the OpenAI Chat target only. OpenAI itself stays off the
list, so its custom tools pass through untouched.
Closes#13789
