Record effective sessions in debug provenance

internal/cli/cache_contract_test.go

@@ -249,10 +249,24 @@ func TestRunAutoReusesPlanWhenRunInputsChange(t *testing.T) {
 	}
 	harness.mu.Lock()
 	chunkCalls := harness.chunkCalls
+	sessions := append([]string(nil), harness.sessionIDs...)
 	harness.mu.Unlock()
 	if chunkCalls != 1 {
 		t.Fatalf("chunk calls across changed run inputs = %d, want 1", chunkCalls)
 	}
+	rawInput, err := os.ReadFile(roots.input)
+	if err != nil {
+		t.Fatal(err)
+	}
+	wantSessionID, err := resolvePromptSessionID("", "test/input", rawInput)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, sessionID := range sessions {
+		if sessionID != wantSessionID {
+			t.Fatalf("session IDs across reference changes = %#v, want %q", sessions, wantSessionID)
+		}
+	}
 	assertFile(t, filepath.Join(roots.plans, strings.TrimPrefix(stateTestDigest, "sha256:"), "plan.json"))
 	assertAnyFile(t, roots.output)
 }