feat(audit): add pricing signature guards and reporting

Add snapshot, signature, and drift guard support for Vertex AI, Cloudflare Workers AI, and Perplexity API, backed by a queryable audit table and recent-window view.

This commit also wires the audit query layer into daily signal materialization and report generation so structure drift becomes a first-class signal instead of a log-only artifact.

scripts/perplexity_pricing_signature_guard_test.go

@@ -0,0 +1,102 @@
+//go:build llm_script
+
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestRunPerplexityPricingSignatureGuardInitializesBaseline(t *testing.T) {
+	tempDir := t.TempDir()
+	baselinePath := filepath.Join(tempDir, "baseline.signature.json")
+
+	result, err := runPerplexityPricingSignatureGuard(perplexityPricingSignatureGuardConfig{
+		URL:            defaultPerplexityPricingFetchURL,
+		Fixture:        filepath.Join("testdata", "perplexity_pricing_sample.md"),
+		SnapshotDir:    tempDir,
+		BaselinePath:   baselinePath,
+		Timeout:        time.Second,
+		AllowBootstrap: true,
+	}, time.Date(2026, 5, 15, 20, 40, 0, 0, time.FixedZone("CST", 8*3600)))
+	if err != nil {
+		t.Fatalf("runPerplexityPricingSignatureGuard 返回错误: %v", err)
+	}
+	if !result.BaselineInitialized {
+		t.Fatalf("期望初始化 baseline")
+	}
+	if result.DriftDetected {
+		t.Fatalf("首次初始化不应判定为漂移")
+	}
+	if _, err := os.Stat(baselinePath); err != nil {
+		t.Fatalf("baseline 未写入: %v", err)
+	}
+}
+
+func TestRunPerplexityPricingSignatureGuardDetectsDrift(t *testing.T) {
+	tempDir := t.TempDir()
+	baselinePath := filepath.Join(tempDir, "baseline.signature.json")
+
+	_, err := runPerplexityPricingSignatureGuard(perplexityPricingSignatureGuardConfig{
+		URL:            defaultPerplexityPricingFetchURL,
+		Fixture:        filepath.Join("testdata", "perplexity_pricing_sample.md"),
+		SnapshotDir:    tempDir,
+		BaselinePath:   baselinePath,
+		Timeout:        time.Second,
+		AllowBootstrap: true,
+	}, time.Date(2026, 5, 15, 20, 41, 0, 0, time.FixedZone("CST", 8*3600)))
+	if err != nil {
+		t.Fatalf("初始化 baseline 失败: %v", err)
+	}
+
+	driftFixture := "# Models\n\n| Name | Pricing |\n| --- | --- |\n| sonar | $1 |\n"
+	driftPath := filepath.Join(tempDir, "perplexity-drift.md")
+	if err := os.WriteFile(driftPath, []byte(driftFixture), 0o644); err != nil {
+		t.Fatalf("写入 drift fixture 失败: %v", err)
+	}
+
+	result, err := runPerplexityPricingSignatureGuard(perplexityPricingSignatureGuardConfig{
+		URL:            defaultPerplexityPricingFetchURL,
+		Fixture:        driftPath,
+		SnapshotDir:    tempDir,
+		BaselinePath:   baselinePath,
+		Timeout:        time.Second,
+		AllowBootstrap: false,
+	}, time.Date(2026, 5, 15, 20, 42, 0, 0, time.FixedZone("CST", 8*3600)))
+	if err == nil {
+		t.Fatalf("期望结构漂移时报错")
+	}
+	if !result.DriftDetected {
+		t.Fatalf("期望 driftDetected=true")
+	}
+	if !strings.Contains(err.Error(), "perplexity pricing structure drift detected") {
+		t.Fatalf("期望返回 drift 错误，实际: %v", err)
+	}
+}
+
+func TestFormatPerplexityPricingSignatureGuardSummary(t *testing.T) {
+	result := perplexityPricingSignatureGuardResult{
+		SnapshotPath:        "/tmp/perplexity.md",
+		SignaturePath:       "/tmp/perplexity.signature.json",
+		BaselinePath:        "/tmp/baseline.signature.json",
+		DriftDetected:       false,
+		BaselineInitialized: true,
+		CurrentSignature: markdownPricingStructureSignature{
+			StructureSHA256: "abc123",
+		},
+	}
+	summary := formatPerplexityPricingSignatureGuardSummary(result)
+	for _, want := range []string{
+		"source=perplexity-pricing-signature-guard",
+		"drift=false",
+		"baseline_initialized=true",
+		"structure_sha256=abc123",
+	} {
+		if !strings.Contains(summary, want) {
+			t.Fatalf("summary 缺少 %q，实际: %q", want, summary)
+		}
+	}
+}