test(tools): verify tenant tool settings flow through media provider chain

Phase 6 of the tenant tool config refactor adopts zero production code
changes for media tools — media_provider_chain.go:77 already reads via
BuiltinToolSettingsFromCtx, and the Phase 3 merge automatically feeds
tenant overrides into that call. This adds 5 verification tests proving
the end-to-end flow: tenant layer beats global, per-agent arg still wins
over tenant, fallback to global when no tenant row, tenant-only layer
works, and cross-tool isolation (create_image override does not leak
into create_audio). Covers the 4-tier overlay on a real tool without
touching any media tool's Execute signature.

internal/tools/media_provider_chain_tenant_test.go

@@ -0,0 +1,130 @@
+package tools
+
+import (
+	"context"
+	"testing"
+
+	"github.com/nextlevelbuilder/goclaw/internal/providers"
+)
+
+// Phase 6 verification: proves the 4-tier overlay (built in Phase 3) flows
+// end-to-end through ResolveMediaProviderChain without any tool-side code
+// change. Tenant-layer settings must override global-layer settings, and
+// per-agent override (arg) must still beat both.
+
+// chainJSON builds a media provider chain settings blob for the given
+// provider name. Single-enabled entry keeps the test assertions terse.
+func chainJSON(provider string) []byte {
+	return []byte(`{"providers":[{"provider":"` + provider + `","model":"m","enabled":true}]}`)
+}
+
+// TestResolveMediaProviderChain_TenantOverrideWins verifies tier-2 tenant
+// bytes take precedence over tier-3 global bytes when both are set for
+// the same tool name. This is the core Phase 6 promise.
+func TestResolveMediaProviderChain_TenantOverrideWins(t *testing.T) {
+	global := BuiltinToolSettings{"create_image": chainJSON("global_provider")}
+	tenant := BuiltinToolSettings{"create_image": chainJSON("tenant_provider")}
+
+	ctx := WithBuiltinToolSettings(context.Background(), global)
+	ctx = WithTenantToolSettings(ctx, tenant)
+
+	chain := ResolveMediaProviderChain(
+		ctx, "create_image",
+		"", "", // no per-agent override
+		[]string{"fallback"}, // hardcoded default priority
+		map[string]string{},
+		providers.NewRegistry(nil),
+	)
+
+	if len(chain) != 1 {
+		t.Fatalf("chain len = %d, want 1 (%v)", len(chain), chain)
+	}
+	if chain[0].Provider != "tenant_provider" {
+		t.Errorf("chain[0].Provider = %q, want tenant_provider (tenant layer must beat global)", chain[0].Provider)
+	}
+}
+
+// TestResolveMediaProviderChain_PerAgentArgBeatsTenant verifies the
+// function-argument per-agent override (passed directly, not via ctx) still
+// wins over tenant ctx settings. This is the top of the precedence ladder.
+func TestResolveMediaProviderChain_PerAgentArgBeatsTenant(t *testing.T) {
+	tenant := BuiltinToolSettings{"create_image": chainJSON("tenant_provider")}
+	ctx := WithTenantToolSettings(context.Background(), tenant)
+
+	chain := ResolveMediaProviderChain(
+		ctx, "create_image",
+		"per_agent_provider", "per_agent_model", // per-agent arg wins
+		[]string{"fallback"},
+		map[string]string{},
+		providers.NewRegistry(nil),
+	)
+
+	if len(chain) != 1 {
+		t.Fatalf("chain len = %d, want 1", len(chain))
+	}
+	if chain[0].Provider != "per_agent_provider" {
+		t.Errorf("chain[0].Provider = %q, want per_agent_provider", chain[0].Provider)
+	}
+}
+
+// TestResolveMediaProviderChain_FallsBackToGlobalWhenNoTenant verifies
+// that with only the global tier set (no tenant ctx key), the function
+// returns the global chain. Backward-compat regression guard.
+func TestResolveMediaProviderChain_FallsBackToGlobalWhenNoTenant(t *testing.T) {
+	global := BuiltinToolSettings{"create_image": chainJSON("global_provider")}
+	ctx := WithBuiltinToolSettings(context.Background(), global)
+
+	chain := ResolveMediaProviderChain(
+		ctx, "create_image",
+		"", "",
+		[]string{"fallback"},
+		map[string]string{},
+		providers.NewRegistry(nil),
+	)
+
+	if len(chain) != 1 || chain[0].Provider != "global_provider" {
+		t.Errorf("chain = %v, want single entry 'global_provider'", chain)
+	}
+}
+
+// TestResolveMediaProviderChain_TenantOnly verifies tenant-layer-only
+// config (no global row) still surfaces. Critical for tenants that want
+// to opt into a provider that's disabled by default.
+func TestResolveMediaProviderChain_TenantOnly(t *testing.T) {
+	tenant := BuiltinToolSettings{"create_image": chainJSON("tenant_provider")}
+	ctx := WithTenantToolSettings(context.Background(), tenant)
+
+	chain := ResolveMediaProviderChain(
+		ctx, "create_image",
+		"", "",
+		[]string{"fallback"},
+		map[string]string{},
+		providers.NewRegistry(nil),
+	)
+
+	if len(chain) != 1 || chain[0].Provider != "tenant_provider" {
+		t.Errorf("chain = %v, want single entry 'tenant_provider'", chain)
+	}
+}
+
+// TestResolveMediaProviderChain_DifferentTools_Independent verifies that
+// tenant settings for one tool (create_image) don't leak into another
+// tool (create_audio) — merge happens at tool-name level.
+func TestResolveMediaProviderChain_DifferentTools_Independent(t *testing.T) {
+	tenant := BuiltinToolSettings{"create_image": chainJSON("image_tenant")}
+	ctx := WithTenantToolSettings(context.Background(), tenant)
+
+	// Query a different tool — tenant has no entry for it.
+	chain := ResolveMediaProviderChain(
+		ctx, "create_audio",
+		"", "",
+		[]string{}, // empty priority — nothing to build
+		map[string]string{},
+		providers.NewRegistry(nil),
+	)
+
+	// No per-agent, no matching tenant key, no global, no hardcoded → empty chain.
+	if len(chain) != 0 {
+		t.Errorf("create_audio chain = %v, want empty (no cross-tool leak)", chain)
+	}
+}