fix(aliases): deterministic integration gate, warn-first fast path, deduped listing

Review fix, task 6 (1 Important + 3 folded):

1. TestModelAliases now polls GET /v1/models (waitForModelAlias) until
   "aliased/mock" appears, bounded 30s, before asserting - removes the
   stale-dynamic-config propagation window a plain healthy-200 check
   cannot rule out. Confirmed config-propagation, not alias-logic, per
   reviewer's config+error-text analysis.
2. registry.go resolve(): check the warned-set (aliasShadowWarned) before
   paying bareWinner's O(providerNames) scan on every aliased request -
   only the first request for a colliding alias pays that cost now.
3. listFor: skip an alias entry whose id already exists in owners (a real
   model already owns it) - previously produced duplicate ids when a
   discovered model collided with a configured alias. resolve's own
   alias-wins precedence is unchanged; only the listing is deduped. New
   test: TestModelRegistry_ListFor_Alias_DedupedAgainstDiscoveredCollision.
4. newAliasTestRegistry doc comment: "grp's given aliases" -> "the given
   aliases" (no grp parameter exists).

registry_test.go

@@ -899,7 +899,7 @@ func TestNewGateway_WarmFill_PopulatesDiscoveredModels_BeforeAnyRequest(t *testi
 // --- model aliases (spec §5, v0.2) ---
 
 // newAliasTestRegistry builds a registry with one "openai" provider
-// (explicit model "gpt-test") and grp's given aliases, failing the test on
+// (explicit model "gpt-test") and the given aliases, failing the test on
 // any construction error. log defaults to a no-op when nil.
 func newAliasTestRegistry(t *testing.T, aliases map[string]string, log func(string, ...any)) *modelRegistry {
 	t.Helper()
@@ -1243,3 +1243,60 @@ func TestModelRegistry_ListFor_Alias_NotAuthorized_Omitted(t *testing.T) {
 		}
 	}
 }
+
+// TestModelRegistry_ListFor_Alias_DedupedAgainstDiscoveredCollision is the
+// review fix for listFor's alias-listing loop: when a provider's
+// discovery fetch finds a model whose bare id is identical to a
+// configured alias id (impossible for an EXPLICIT model —
+// validateModelAliases already rejects that at construction, but
+// discovery is dynamic and runs after that check), the listing must show
+// exactly ONE entry for that id — not one from the real discovered model
+// and a second, duplicate one from the alias loop. resolve's own
+// precedence (registry.go's resolve doc comment) must still have the
+// alias win at request time regardless of which entry the listing shows.
+func TestModelRegistry_ListFor_Alias_DedupedAgainstDiscoveredCollision(t *testing.T) {
+	t.Parallel()
+	adapters := map[string]providerAdapter{
+		"openai": newFakeAdapter("openai"),
+		"acme":   newFakeAdapter("acme"),
+	}
+	cfg := &Config{
+		Providers: map[string]*ProviderConfig{
+			"openai": {Models: []string{"gpt-test"}},
+			"acme":   {Discovery: true},
+		},
+		ModelAliases: map[string]string{"shared-id": "openai/gpt-test"},
+	}
+	reg, err := newModelRegistry(adapters, cfg, func(string, ...any) {})
+	if err != nil {
+		t.Fatalf("newModelRegistry: %v", err)
+	}
+	// acme's discovery finds a model literally named "shared-id" — the
+	// same string as the configured alias, discovered only after
+	// construction, so validateModelAliases never saw it.
+	reg.states["acme"].finishRefresh(reg.now(), []string{"shared-id"}, nil)
+
+	got := reg.listFor(allowAllGroup())
+	count := 0
+	for _, entry := range got {
+		if entry["id"] == "shared-id" {
+			count++
+		}
+	}
+	if count != 1 {
+		t.Errorf("listFor has %d entries for id %q, want exactly 1 (deduped)", count, "shared-id")
+	}
+
+	// resolve must still prefer the alias, per its documented precedence,
+	// regardless of which single entry the listing showed above.
+	adapter, _, canonical, err := reg.resolve("shared-id", allowAllGroup())
+	if err != nil {
+		t.Fatalf("resolve: %v", err)
+	}
+	if adapter != adapters["openai"] {
+		t.Errorf("adapter = %v, want openai (the alias, not acme's discovered model, must still win resolution)", adapter)
+	}
+	if canonical != "openai/gpt-test" {
+		t.Errorf("canonical = %q, want %q", canonical, "openai/gpt-test")
+	}
+}