[bug]: transport 502 echoes base_url including ?key=

[Atharva-Kanherkar]

symptom

switchyard-server 0.2.0 copies reqwest's transport error into the client 502. that string includes the full upstream url. if the admin put the provider key in base_url as ?key= (google's documented gemini shape), the caller gets the key.

header bearer keys and http userinfo (http://key@host) are not echoed. query params are.

reproduction

no server listening on 19998.

schema_version = 1
[llm_clients.local]
format = "openai_chat"
base_url = "http://127.0.0.1:19998/v1?key=CANARY_ADMIN_QUERY_KEY"
[llm_clients.local.extra_headers]
authorization = "Bearer CANARY_ADMIN_HEADER_KEY"
[targets.cap]
id = "captured-model"
llm_client = "local"
[routes.primary]
id = "captured-model"
type = "passthrough"
target = "cap"

switchyard-server --config sy.toml --port 9000
curl -s localhost:9000/v1/chat/completions \
  -H 'content-type: application/json' \
  -d '{"model":"captured-model","messages":[{"role":"user","content":"x"}],"max_tokens":8}'

actual: http 502. error.message is:

error sending request for url (http://127.0.0.1:19998/v1?key=CANARY_ADMIN_QUERY_KEY/chat/completions)

5/5. a 502 whose base_url has no query string does not contain the canary. a successful chat does not either. /health, /v1/models, /v1/stats stay clean.

expected vs. actual

• expected: client-visible errors do not contain credentials from base_url.
• actual: ?key= stays in the url string. the extra_headers bearer is not echoed.

environment

• switchyard version (or commit sha): 0.2.0 (commit 2bef154)
• python version (python --version): n/a (rust switchyard-server)
• os / arch: macos arm64
• install path: source build cargo build --release -p switchyard-server
• inbound format (chat completions / anthropic messages / responses): chat completions, also stream and /v1/messages
• backend (openai / anthropic / nvidia inference hub / other): closed local port (transport failure). live header-auth chats to openai/gemini/anthropic/openrouter did not echo the bearer.

additional context

client_error maps LlmClientError::Transport / Timeout to source.to_string(). reqwest includes the url. there is no redaction step. HttpBackendConfig's Debug impl redacts api_key, but that is not the path the client sees.

this is a canary-only report. no real provider keys in the public captures.

wire captures and replay tests: Atharva-Kanherkar/kairo#6