refactor: gadfly round 3 — one table owns the OpenAI-compat contract

Three findings, and the first two are the same recurring shape.

envKeyForProvider (env.go) is now the single definition of the LLM_<NAME>
form. It lived in two places — lazy resolution in registry.go and the
missing-key hint in openaiCompatScheme — with a comment on the second asserting
it matched the first. A comment is not enforcement: if either had drifted, a
keyless DSN target would have named a variable that does nothing, and nothing
would have failed.

The kimi and qwen test files had become near-identical, which is round 1's
finding at the level above it: I deduped the fixtures, then left two parallel
suites asserting the same four things. They are now ONE table in
builtin_openaicompat_test.go — endpoint + credential, missing key fails closed
naming its own variable and never reaching the network, the name:// DSN
reaching another host, and a keyless DSN naming LLM_<NAME> instead of the
built-in's key. Adding an OpenAI-compat built-in is a table row that
immediately owes all four; builtin_kimi_test.go is deleted because the table
covers it. Only genuinely qwen-specific tests remain in the qwen file: the
reverse credential leak and the reasoning_effort wire claim ADR-0027 rests on.

Also trimmed ProviderQwen's doc comment, which restated the ADR-0027 rationale
already given at the registration site.

The break-check suite caught its own rot again — two mutations went stale when
these tests were renamed, and the landed-check reported them loudly instead of
passing them off as green. Now 9 cases, including one that drifts
envKeyForProvider to prove the shared helper is load-bearing. 9/9 apply and are
caught.

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

builtin.go

@@ -2,7 +2,6 @@ package majordomo
 
 import (
 	"net/http"
-	"strings"
 
 	"gitea.stevedudenhoeffer.com/steve/majordomo/llm"
 	"gitea.stevedudenhoeffer.com/steve/majordomo/provider/anthropic"
@@ -22,11 +21,8 @@ const (
 	// ProviderQwen is Alibaba's Qwen models over Model Studio's
 	// OpenAI-compatible Chat Completions endpoint. Reuses the openai client
 	// (like kimi and llama-swap); keyed by QWEN_API_KEY, default base URL
-	// qwenBaseURL. Why OpenAI-compat and not the Anthropic-compat endpoint
-	// Model Studio also exposes: see ADR-0027 — the OpenAI surface is the
-	// first-class one there (reasoning_effort, json_schema structured output,
-	// cached_tokens accounting all ride it), while the Anthropic shim exists
-	// mainly to host Claude Code.
+	// qwenBaseURL. ADR-0027 records why the OpenAI surface and not the
+	// Anthropic-compatible one Model Studio also exposes.
 	ProviderQwen        = "qwen"
 	ProviderAnthropic   = "anthropic"
 	ProviderGoogle      = "google"
@@ -67,7 +63,7 @@ func openaiCompatScheme(wrap func(...openai.Option) []openai.Option) SchemeFacto
 			openai.WithName(name),
 			openai.WithBaseURL(dsn.BaseURL()),
 			openai.WithAPIKey(dsn.Token),
-			openai.WithAPIKeyName("LLM_"+strings.ToUpper(strings.ReplaceAll(name, "-", "_"))),
+			openai.WithAPIKeyName(envKeyForProvider(name)),
 		)...), nil
 	}
 }