Hoist the Upgrade->501 and traversal->400 checks in handleTargetProxy
above checkAndCount, matching handlePassthrough's own order
(403 -> 501 -> 400 -> limit). A request rejected before the upstream
call must never burn the caller's or their group's rate-limit quota
for a call that was never going to reach the target. Updated the
function's doc comment to state and justify the order.
Add TestHandleTargetProxy_RateLimited_Returns429WithRetryAfter:
group requestsPerMinute:1, two hits on /mcp/{name}/x -> first 200,
second 429 with Retry-After, upstream called exactly once.
Add TestHandleTargetProxy_JSONResponse_OnlyRequestCounterMoves: a
usage-shaped JSON response from the target leaves token/cost
counters at 0 while the request-rate counter moves to 1, proving
the target proxy never tees or accounts a response the way native
passthrough does.
Add GET /v1/mcp/servers and GET /v1/agents: group-filtered,
name-sorted registry listings of configured MCP servers and A2A
agents, with their gateway-relative proxy (and, for agents, card)
URLs.
Add handleTargetProxy for /mcp/{name}/{rest...} and
/a2a/{name}/{rest...}: reverse-proxies to the target's configured
URL. Checks run unknown name (404), group deny via allowsMCP/
allowsAgent (403), request-rate limits (429/503), then Upgrade
(501) and path traversal (400) around the proxy call itself. No
upstream credential is injected — MCP servers and A2A agents are
in-cluster targets, unlike native provider passthrough.
Extract proxyUpstream from routes_passthrough.go's handlePassthrough
into a shared reverse-proxy core (header stripping, SSE-safe
flushWriter streaming, dead-upstream 502, canceled-client log-only,
optional JSON usage teeing) used by both native passthrough and the
new target proxy. Behavior-preserving for Task 13: its tests pass
unmodified.
Validate every configured MCP-server and agent target URL at
construction (url.Parse, http/https scheme only) — a malformed or
non-HTTP target is a constructor error, not a per-request 502.
lukaszraczylo