feat(agent): identify Go SDK traffic in user agent

[LukasParke]

Appends the go-agent module path to the generated SDK's User-Agent so agent traffic is distinguishable from plain go-sdk traffic.

speakeasy-sdk/go 0.5.4 2.879.6 1.0.0 github.com/OpenRouterTeam/go-sdk github.com/OpenRouterTeam/go-agent/0.8.0

Behavior

• The token is resolved once in NewOpenRouter via debug.ReadBuildInfo(), checking the main module then deps. A consumer build yields github.com/OpenRouterTeam/go-agent/<version>; a (devel) or version-less build yields the bare module path.
• The header is set before the before-request hooks run, so caller middleware that rewrites User-Agent still wins.
• Appending is idempotent — a retried *http.Request does not accumulate duplicate tokens.

Language-specific identity

.upstreamer/upstreamer.md gains divergence #7: Go appends the module path, TypeScript the npm package name (@openrouter/agent), Python the PyPI distribution name (openrouter-agent-sdk). The porting automation must not converge this token toward the TypeScript literal.

Tests

Four unit tests cover append, idempotence, caller override, and agentUserAgentTokenFromBuildInfo across five build-info shapes.

Added on top of the original patch: TestNewOpenRouterSendsAgentUserAgentOnTheWire. The four unit tests construct middlewareClient directly with a hardcoded token, so none of them exercise NewOpenRouter's wiring or prove the header survives the full SDK path. The new test drives NewOpenRouter through CallModel against a recording transport and asserts the agent token arrives last with the generated SDK token preserved.

Mutation-checked for teeth: deleting the req.Header.Set in Do fails both it and the unit test. Note that removing agentToken: agentUserAgentToken() from NewOpenRouter does not fail anything — Do's if agentToken == "" fallback recomputes it, so the constructor assignment is a per-request optimization rather than a correctness path.

Verification

gofmt -l .                                    clean
go build ./... / go vet ./...                 pass
go test -race -shuffle=on -count=1 ./...      pass
staticcheck ./...                             clean
.upstreamer/scripts/verify.sh                 PASS: 0 failures (coverage 72.4% >= 72.0%)
env -u OPENROUTER_API_KEY go test -run TestE2E  SKIP (not fail)