feat(07-03): dedup helper for imported findings

- FindingKey: stable SHA-256 over provider+masked+source+line
- Dedup: preserves first-seen order, returns drop count
- 8 unit tests covering stability, field sensitivity, order preservation

pkg/importer/dedup_test.go

@@ -0,0 +1,106 @@
+package importer
+
+import (
+	"testing"
+	"time"
+
+	"github.com/salvacybersec/keyhunter/pkg/engine"
+)
+
+func mkFinding(provider, masked, source string, line int) engine.Finding {
+	return engine.Finding{
+		ProviderName: provider,
+		KeyMasked:    masked,
+		Source:       source,
+		LineNumber:   line,
+	}
+}
+
+func TestFindingKey_Stable(t *testing.T) {
+	f := mkFinding("openai", "sk-abc12...wxyz", "src/app.go", 42)
+	if FindingKey(f) != FindingKey(f) {
+		t.Fatal("FindingKey must be deterministic for identical input")
+	}
+}
+
+func TestFindingKey_DiffersByProvider(t *testing.T) {
+	a := mkFinding("openai", "sk-abc12...wxyz", "src/app.go", 42)
+	b := mkFinding("anthropic", "sk-abc12...wxyz", "src/app.go", 42)
+	if FindingKey(a) == FindingKey(b) {
+		t.Fatal("different providers must yield different keys")
+	}
+}
+
+func TestFindingKey_DiffersByMasked(t *testing.T) {
+	a := mkFinding("openai", "sk-aaaaa...wxyz", "src/app.go", 42)
+	b := mkFinding("openai", "sk-bbbbb...wxyz", "src/app.go", 42)
+	if FindingKey(a) == FindingKey(b) {
+		t.Fatal("different masked keys must yield different keys")
+	}
+}
+
+func TestFindingKey_DiffersBySource(t *testing.T) {
+	a := mkFinding("openai", "sk-abc12...wxyz", "src/app.go", 42)
+	b := mkFinding("openai", "sk-abc12...wxyz", "src/other.go", 42)
+	if FindingKey(a) == FindingKey(b) {
+		t.Fatal("different sources must yield different keys")
+	}
+}
+
+func TestFindingKey_DiffersByLine(t *testing.T) {
+	a := mkFinding("openai", "sk-abc12...wxyz", "src/app.go", 42)
+	b := mkFinding("openai", "sk-abc12...wxyz", "src/app.go", 43)
+	if FindingKey(a) == FindingKey(b) {
+		t.Fatal("different line numbers must yield different keys")
+	}
+}
+
+func TestDedup_PreservesOrder(t *testing.T) {
+	a := mkFinding("openai", "sk-aaa...0001", "file_a.go", 1)
+	b := mkFinding("openai", "sk-bbb...0002", "file_b.go", 2)
+	c := mkFinding("openai", "sk-ccc...0003", "file_c.go", 3)
+	in := []engine.Finding{a, b, a, c, b}
+
+	out, dropped := Dedup(in)
+
+	if dropped != 2 {
+		t.Fatalf("expected 2 dropped, got %d", dropped)
+	}
+	if len(out) != 3 {
+		t.Fatalf("expected 3 unique, got %d", len(out))
+	}
+	if out[0].KeyMasked != a.KeyMasked || out[1].KeyMasked != b.KeyMasked || out[2].KeyMasked != c.KeyMasked {
+		t.Fatalf("dedup did not preserve first-seen order: %+v", out)
+	}
+}
+
+func TestDedup_Empty(t *testing.T) {
+	out, dropped := Dedup(nil)
+	if dropped != 0 {
+		t.Fatalf("expected 0 dropped, got %d", dropped)
+	}
+	if len(out) != 0 {
+		t.Fatalf("expected empty output, got %d", len(out))
+	}
+}
+
+func TestDedup_IgnoresUnrelatedFields(t *testing.T) {
+	base := mkFinding("openai", "sk-abc12...wxyz", "src/app.go", 42)
+	base.DetectedAt = time.Now()
+	base.Confidence = "high"
+
+	twin := mkFinding("openai", "sk-abc12...wxyz", "src/app.go", 42)
+	twin.DetectedAt = base.DetectedAt.Add(24 * time.Hour)
+	twin.Confidence = "low"
+
+	out, dropped := Dedup([]engine.Finding{base, twin})
+	if dropped != 1 {
+		t.Fatalf("expected 1 dropped, got %d", dropped)
+	}
+	if len(out) != 1 {
+		t.Fatalf("expected 1 kept, got %d", len(out))
+	}
+	if out[0].Confidence != "high" {
+		t.Fatalf("expected first-seen to be kept, got Confidence=%s", out[0].Confidence)
+	}
+}