refactor(test): gadfly round 1 — share the OpenAI-compat test fixtures

Both findings were the same one, and both were fair: the PR that retires two
byte-identical DSN factories into openaiCompatScheme then copy-pasted the test
fixtures. qwenResponse was byte-identical to kimiResponse, and the single-key
env-lookup closure appeared three times in the new file (plus a fourth in the
kimi file, which neither reviewer was looking at).

Fixed for the class rather than for qwen: captureRT, the canned Chat
Completions body (now chatCompletionOK), and a new singleKeyEnv helper move to
builtin_openaicompat_test.go, owned by no single provider. The kimi tests adopt
them too, so the next OpenAI-compat built-in has nothing left to copy — the
same argument the production helper makes.

Also aligned the test model ids to the current Model Studio names
(qwen3.8-max / qwen3.7-plus), which the docs already cited. One reviewer called
those ids fictional and named the 2025 ones instead; they shipped 2026-08-03
and 2026-05-21 respectively, so that finding is stale model knowledge, not a
defect — but having tests and prose name the same models removes the smell that
prompted it. A dotted id also now proves it passes through verbatim.

Break-checked again after the refactor: all six mutations still fail their test.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

builtin_kimi_test.go

@@ -3,7 +3,6 @@ package majordomo
 import (
 	"context"
 	"errors"
-	"io"
 	"net/http"
 	"strings"
 	"testing"
@@ -11,49 +10,12 @@ import (
 	"gitea.stevedudenhoeffer.com/steve/majordomo/llm"
 )
 
-// kimiResponse is a minimal valid Chat Completions body so Generate returns a
-// non-empty response (an empty one would trigger failover, not a clean pass).
-const kimiResponse = `{"id":"c1","object":"chat.completion","choices":[` +
-	`{"index":0,"message":{"role":"assistant","content":"ok"},"finish_reason":"stop"}]}`
-
-// captureRT records the last request (and the bytes of its body) and returns a
-// canned response without touching the network, so these tests stay hermetic
-// while still exercising the real openai client the kimi and qwen built-ins
-// reuse: base URL, auth header, and the JSON actually put on the wire.
-type captureRT struct {
-	req     *http.Request
-	reqBody []byte
-	body    string
-}
-
-func (c *captureRT) RoundTrip(r *http.Request) (*http.Response, error) {
-	c.req = r
-	// Drain and close the request body: a RoundTripper owns it, and those
-	// bytes are what wire-shape assertions read.
-	c.reqBody = nil
-	if r.Body != nil {
-		c.reqBody, _ = io.ReadAll(r.Body)
-		_ = r.Body.Close()
-	}
-	return &http.Response{
-		StatusCode: http.StatusOK,
-		Body:       io.NopCloser(strings.NewReader(c.body)),
-		Header:     make(http.Header),
-		Request:    r,
-	}, nil
-}
-
 // TestKimiBuiltin: the built-in "kimi" provider resolves in Parse, targets
 // Moonshot's default endpoint, and authenticates with KIMI_API_KEY.
 func TestKimiBuiltin(t *testing.T) {
-	rt := &captureRT{body: kimiResponse}
+	rt := &captureRT{body: chatCompletionOK}
 	r := newTestRegistry(t,
-		WithEnvLookup(func(k string) string {
-			if k == "KIMI_API_KEY" {
-				return "kimi-secret"
-			}
-			return ""
-		}),
+		WithEnvLookup(singleKeyEnv("KIMI_API_KEY", "kimi-secret")),
 		WithHTTPClient(&http.Client{Transport: rt}),
 	)
 
@@ -90,7 +52,7 @@ func TestKimiBuiltin(t *testing.T) {
 // the credential does not fall through to the openai client's default), and
 // without hitting the network.
 func TestKimiBuiltinMissingKey(t *testing.T) {
-	rt := &captureRT{body: kimiResponse}
+	rt := &captureRT{body: chatCompletionOK}
 	r := newTestRegistry(t, WithHTTPClient(&http.Client{Transport: rt}))
 
 	m, err := r.Parse("kimi/kimi-k2-0711-preview")
@@ -120,7 +82,7 @@ func TestKimiBuiltinMissingKey(t *testing.T) {
 // host (here the China endpoint) that is first-class in Parse and carries the
 // DSN token as its bearer credential.
 func TestKimiScheme(t *testing.T) {
-	rt := &captureRT{body: kimiResponse}
+	rt := &captureRT{body: chatCompletionOK}
 	r := newTestRegistry(t, WithHTTPClient(&http.Client{Transport: rt}))
 	if err := r.LoadEnv(map[string]string{
 		"LLM_KCN": "kimi://[email protected]/v1",
@@ -151,7 +113,7 @@ func TestKimiScheme(t *testing.T) {
 // defining LLM_<NAME> env var, never KIMI_API_KEY (which does nothing for a
 // DSN-defined provider).
 func TestKimiSchemeMissingToken(t *testing.T) {
-	rt := &captureRT{body: kimiResponse}
+	rt := &captureRT{body: chatCompletionOK}
 	r := newTestRegistry(t, WithHTTPClient(&http.Client{Transport: rt}))
 	if err := r.LoadEnv(map[string]string{
 		"LLM_KCN": "kimi://api.moonshot.cn/v1", // no token