diff --git a/cmd/opencodereview/emit_run_result_test.go b/cmd/opencodereview/emit_run_result_test.go
index 3770fee..6ad71bb 100644
--- a/cmd/opencodereview/emit_run_result_test.go
+++ b/cmd/opencodereview/emit_run_result_test.go
@@ -181,7 +181,7 @@ func TestEmitRunResult_NilQuietHandle(t *testing.T) {
 
 func TestEmitRunResult_JSONTraceIDFromContext(t *testing.T) {
 	tp := sdktrace.NewTracerProvider()
-	defer tp.Shutdown(context.Background())
+	defer func() { _ = tp.Shutdown(context.Background()) }()
 	otel.SetTracerProvider(tp)
 
 	ctx, span := tp.Tracer("test").Start(context.Background(), "test-root")
@@ -211,7 +211,7 @@ func TestEmitRunResult_JSONTraceIDFromContext(t *testing.T) {
 
 func TestEmitRunResult_JSONNoFilesTraceID(t *testing.T) {
 	tp := sdktrace.NewTracerProvider()
-	defer tp.Shutdown(context.Background())
+	defer func() { _ = tp.Shutdown(context.Background()) }()
 	otel.SetTracerProvider(tp)
 
 	ctx, span := tp.Tracer("test").Start(context.Background(), "test-root")
diff --git a/cmd/opencodereview/git_test.go b/cmd/opencodereview/git_test.go
index 0630a4c..4528b29 100644
--- a/cmd/opencodereview/git_test.go
+++ b/cmd/opencodereview/git_test.go
@@ -23,11 +23,17 @@ func initTestGitRepo(t *testing.T) string {
 		}
 	}
 	f := filepath.Join(dir, "README.md")
-	os.WriteFile(f, []byte("hello"), 0o644)
+	if err := os.WriteFile(f, []byte("hello"), 0o644); err != nil {
+		t.Fatalf("write README: %v", err)
+	}
 	cmd := exec.Command("git", "-C", dir, "add", ".")
-	cmd.CombinedOutput()
+	if out, err := cmd.CombinedOutput(); err != nil {
+		t.Fatalf("git add: %v: %s", err, out)
+	}
 	cmd = exec.Command("git", "-C", dir, "commit", "-m", "initial commit")
-	cmd.CombinedOutput()
+	if out, err := cmd.CombinedOutput(); err != nil {
+		t.Fatalf("git commit: %v: %s", err, out)
+	}
 	return dir
 }
 
@@ -93,9 +99,18 @@ func TestResolveRepoDir_NotGitRepo(t *testing.T) {
 
 func TestResolveRepoDir_EmptyUsesWd(t *testing.T) {
 	dir := initTestGitRepo(t)
-	origDir, _ := os.Getwd()
-	defer os.Chdir(origDir)
-	os.Chdir(dir)
+	origDir, err := os.Getwd()
+	if err != nil {
+		t.Fatalf("getwd: %v", err)
+	}
+	defer func() {
+		if err := os.Chdir(origDir); err != nil {
+			t.Errorf("restore chdir: %v", err)
+		}
+	}()
+	if err := os.Chdir(dir); err != nil {
+		t.Fatalf("chdir: %v", err)
+	}
 
 	resolved, err := resolveRepoDir("")
 	if err != nil {
diff --git a/cmd/opencodereview/output_helpers_test.go b/cmd/opencodereview/output_helpers_test.go
index f3d9127..31001e7 100644
--- a/cmd/opencodereview/output_helpers_test.go
+++ b/cmd/opencodereview/output_helpers_test.go
@@ -169,7 +169,7 @@ func TestOutputJSONWithWarnings_NoCommentsSubtaskError(t *testing.T) {
 
 	warnings := []agent.AgentWarning{{Type: "subtask_error", File: "x.go", Message: "fail"}}
 	err := outputJSONWithWarnings(nil, warnings, 1, 10, 5, 15, 0, 0, time.Second, "", nil, "abc123trace")
-	w.Close()
+	_ = w.Close()
 	os.Stdout = old
 
 	if err != nil {
@@ -177,10 +177,12 @@ func TestOutputJSONWithWarnings_NoCommentsSubtaskError(t *testing.T) {
 	}
 
 	var buf bytes.Buffer
-	buf.ReadFrom(r)
+	_, _ = buf.ReadFrom(r)
 
 	var out jsonOutput
-	json.Unmarshal(buf.Bytes(), &out)
+	if err := json.Unmarshal(buf.Bytes(), &out); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
 	if out.Status != "completed_with_errors" {
 		t.Errorf("status = %q, want completed_with_errors", out.Status)
 	}
@@ -224,7 +226,7 @@ func TestOutputJSON(t *testing.T) {
 	}
 	err := outputJSON(comments)
 
-	w.Close()
+	_ = w.Close()
 	os.Stdout = old
 
 	if err != nil {
@@ -232,7 +234,7 @@ func TestOutputJSON(t *testing.T) {
 	}
 
 	var buf bytes.Buffer
-	buf.ReadFrom(r)
+	_, _ = buf.ReadFrom(r)
 
 	var out jsonOutput
 	if err := json.Unmarshal(buf.Bytes(), &out); err != nil {
@@ -253,7 +255,7 @@ func TestOutputJSON_NoComments(t *testing.T) {
 
 	err := outputJSON(nil)
 
-	w.Close()
+	_ = w.Close()
 	os.Stdout = old
 
 	if err != nil {
@@ -261,10 +263,12 @@ func TestOutputJSON_NoComments(t *testing.T) {
 	}
 
 	var buf bytes.Buffer
-	buf.ReadFrom(r)
+	_, _ = buf.ReadFrom(r)
 
 	var out jsonOutput
-	json.Unmarshal(buf.Bytes(), &out)
+	if err := json.Unmarshal(buf.Bytes(), &out); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
 	if out.Message == "" {
 		t.Error("expected non-empty message when no comments")
 	}
@@ -278,7 +282,7 @@ func TestOutputJSONWithWarnings(t *testing.T) {
 	comments := []model.LlmComment{{Path: "b.go", Content: "test"}}
 	warnings := []agent.AgentWarning{{Type: "subtask_error", File: "c.go", Message: "failed"}}
 	err := outputJSONWithWarnings(comments, warnings, 5, 100, 50, 150, 10, 5, 3*time.Second, "summary", map[string]int64{"file_read": 3}, "trace-xyz-789")
-	w.Close()
+	_ = w.Close()
 	os.Stdout = old
 
 	if err != nil {
@@ -286,10 +290,12 @@ func TestOutputJSONWithWarnings(t *testing.T) {
 	}
 
 	var buf bytes.Buffer
-	buf.ReadFrom(r)
+	_, _ = buf.ReadFrom(r)
 
 	var out jsonOutput
-	json.Unmarshal(buf.Bytes(), &out)
+	if err := json.Unmarshal(buf.Bytes(), &out); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
 	if out.Status != "completed_with_errors" {
 		t.Errorf("status = %q, want completed_with_errors", out.Status)
 	}
@@ -314,7 +320,7 @@ func TestOutputJSONWithWarnings_NoCommentsNoErrors(t *testing.T) {
 
 	warnings := []agent.AgentWarning{{Type: "warning", Message: "something"}}
 	err := outputJSONWithWarnings(nil, warnings, 2, 50, 20, 70, 0, 0, time.Second, "", nil, "")
-	w.Close()
+	_ = w.Close()
 	os.Stdout = old
 
 	if err != nil {
@@ -322,10 +328,12 @@ func TestOutputJSONWithWarnings_NoCommentsNoErrors(t *testing.T) {
 	}
 
 	var buf bytes.Buffer
-	buf.ReadFrom(r)
+	_, _ = buf.ReadFrom(r)
 
 	var out jsonOutput
-	json.Unmarshal(buf.Bytes(), &out)
+	if err := json.Unmarshal(buf.Bytes(), &out); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
 	if out.Status != "completed_with_warnings" {
 		t.Errorf("status = %q, want completed_with_warnings", out.Status)
 	}
@@ -341,7 +349,7 @@ func TestOutputJSONNoFiles(t *testing.T) {
 
 	err := outputJSONNoFiles("test-trace-id-456")
 
-	w.Close()
+	_ = w.Close()
 	os.Stdout = old
 
 	if err != nil {
@@ -349,10 +357,12 @@ func TestOutputJSONNoFiles(t *testing.T) {
 	}
 
 	var buf bytes.Buffer
-	buf.ReadFrom(r)
+	_, _ = buf.ReadFrom(r)
 
 	var out jsonOutput
-	json.Unmarshal(buf.Bytes(), &out)
+	if err := json.Unmarshal(buf.Bytes(), &out); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
 	if out.Status != "skipped" {
 		t.Errorf("status = %q, want skipped", out.Status)
 	}
@@ -370,10 +380,10 @@ func captureStdout(t *testing.T, fn func()) string {
 	}
 	os.Stdout = w
 	fn()
-	w.Close()
+	_ = w.Close()
 	os.Stdout = old
 	var buf bytes.Buffer
-	buf.ReadFrom(r)
+	_, _ = buf.ReadFrom(r)
 	return buf.String()
 }
 
diff --git a/cmd/opencodereview/output_test.go b/cmd/opencodereview/output_test.go
index c5b8487..038cd84 100644
--- a/cmd/opencodereview/output_test.go
+++ b/cmd/opencodereview/output_test.go
@@ -93,8 +93,8 @@ func TestSanitizeTerminal(t *testing.T) {
 		{"only control chars", "\x1b\x07\x00\x7f", ""},
 		{"unicode preserved", "代码审查 レビュー 🔍", "代码审查 レビュー 🔍"},
 		{"mixed safe and unsafe", "path\x1b[0m/file.go", "path[0m/file.go"},
-		{"strips C1 CSI (U+009B)", "before›after", "beforeafter"},
-		{"strips C1 OSC (U+009D)", "beforeafter", "beforeafter"},
+		{"strips C1 CSI (U+009B)", "before\u009bafter", "beforeafter"},
+		{"strips C1 OSC (U+009D)", "before\u009dafter", "beforeafter"},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
diff --git a/cmd/opencodereview/provider_cmd_test.go b/cmd/opencodereview/provider_cmd_test.go
index e8d84db..d1f03bb 100644
--- a/cmd/opencodereview/provider_cmd_test.go
+++ b/cmd/opencodereview/provider_cmd_test.go
@@ -364,7 +364,7 @@ func TestPrintWizardCancelled(t *testing.T) {
 			}
 			os.Stdout = w
 			printWizardCancelled(tc.savedInSession, tc.scope)
-			w.Close()
+			_ = w.Close()
 			os.Stdout = old
 			got, err := io.ReadAll(r)
 			if err != nil {
diff --git a/cmd/opencodereview/provider_tui_test.go b/cmd/opencodereview/provider_tui_test.go
index 4c9de47..624bc50 100644
--- a/cmd/opencodereview/provider_tui_test.go
+++ b/cmd/opencodereview/provider_tui_test.go
@@ -2169,7 +2169,7 @@ func TestProviderTUI_ApiKeyTypingShowsOneStarPerChar(t *testing.T) {
 	m.loadExistingAPIKey()
 	m.apiKeyInput.Focus()
 
-	for _, ch := range []rune("abc") {
+	for _, ch := range "abc" {
 		result, _ := m.Update(charKey(ch))
 		m = result.(providerTUIModel)
 	}
diff --git a/cmd/opencodereview/shared_test.go b/cmd/opencodereview/shared_test.go
index 21e7553..417a65f 100644
--- a/cmd/opencodereview/shared_test.go
+++ b/cmd/opencodereview/shared_test.go
@@ -79,9 +79,18 @@ func TestQuietHandle_IdempotentRestore(t *testing.T) {
 
 func TestResolveWorkingDir_CurrentDir(t *testing.T) {
 	dir := t.TempDir()
-	origDir, _ := os.Getwd()
-	defer os.Chdir(origDir)
-	os.Chdir(dir)
+	origDir, err := os.Getwd()
+	if err != nil {
+		t.Fatalf("getwd: %v", err)
+	}
+	defer func() {
+		if err := os.Chdir(origDir); err != nil {
+			t.Errorf("restore chdir: %v", err)
+		}
+	}()
+	if err := os.Chdir(dir); err != nil {
+		t.Fatalf("chdir: %v", err)
+	}
 
 	absPath, isGit, err := resolveWorkingDir("", false)
 	if err != nil {
diff --git a/internal/agent/util_test.go b/internal/agent/util_test.go
index af3b8ff..caf030c 100644
--- a/internal/agent/util_test.go
+++ b/internal/agent/util_test.go
@@ -157,6 +157,9 @@ func TestCopyMessages(t *testing.T) {
 	}
 
 	cp = append(cp, llm.NewTextMessage("user", "c"))
+	if len(cp) != len(orig)+1 {
+		t.Errorf("appended copy length = %d, want %d", len(cp), len(orig)+1)
+	}
 	if len(orig) != 2 {
 		t.Error("copyMessages: appending to copy modified original slice")
 	}
diff --git a/internal/config/toolsconfig/toolsconfig_test.go b/internal/config/toolsconfig/toolsconfig_test.go
index bd25bb1..ce6bf30 100644
--- a/internal/config/toolsconfig/toolsconfig_test.go
+++ b/internal/config/toolsconfig/toolsconfig_test.go
@@ -31,7 +31,9 @@ func TestLoad_CustomFile(t *testing.T) {
 	data := `[
 		{"name": "test_tool", "plan_task": true, "main_task": false, "definition": {"name": "test_tool"}}
 	]`
-	os.WriteFile(path, []byte(data), 0644)
+	if err := os.WriteFile(path, []byte(data), 0644); err != nil {
+		t.Fatalf("write tools.json: %v", err)
+	}
 
 	tools, err := Load(path)
 	if err != nil {
@@ -61,7 +63,9 @@ func TestLoad_FileNotFound(t *testing.T) {
 func TestLoad_InvalidJSON(t *testing.T) {
 	tmp := t.TempDir()
 	path := filepath.Join(tmp, "tools.json")
-	os.WriteFile(path, []byte("not json"), 0644)
+	if err := os.WriteFile(path, []byte("not json"), 0644); err != nil {
+		t.Fatalf("write tools.json: %v", err)
+	}
 
 	_, err := Load(path)
 	if err == nil {
diff --git a/internal/llm/message_test.go b/internal/llm/message_test.go
index 53ee185..4a03499 100644
--- a/internal/llm/message_test.go
+++ b/internal/llm/message_test.go
@@ -243,7 +243,9 @@ func TestParseShellRC_ModelOverride(t *testing.T) {
 export ANTHROPIC_AUTH_TOKEN="token"
 export ANTHROPIC_MODEL=claude-3-opus
 `
-	os.WriteFile(rcPath, []byte(content), 0644)
+	if err := os.WriteFile(rcPath, []byte(content), 0644); err != nil {
+		t.Fatalf("write rc: %v", err)
+	}
 
 	ep, ok, err := parseShellRC(rcPath, "override-model")
 	if err != nil {
@@ -265,7 +267,9 @@ func TestParseShellRC_Incomplete(t *testing.T) {
 export ANTHROPIC_AUTH_TOKEN="token"
 # missing ANTHROPIC_MODEL
 `
-	os.WriteFile(rcPath, []byte(content), 0644)
+	if err := os.WriteFile(rcPath, []byte(content), 0644); err != nil {
+		t.Fatalf("write rc: %v", err)
+	}
 
 	_, ok, err := parseShellRC(rcPath, "")
 	if err != nil {
diff --git a/internal/llm/resolver_test.go b/internal/llm/resolver_test.go
index 5b2cace..6c933aa 100644
--- a/internal/llm/resolver_test.go
+++ b/internal/llm/resolver_test.go
@@ -104,7 +104,9 @@ func TestResolveEndpoint_ConfigFileStripsModelSuffix(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	ep, err := ResolveEndpoint(cfgPath)
 	if err != nil {
@@ -137,7 +139,9 @@ func TestResolveEndpoint_ConfigAnthropicDefaultsToAuthorization(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	ep, err := ResolveEndpoint(cfgPath)
 	if err != nil {
@@ -168,7 +172,9 @@ func TestResolveEndpoint_ConfigAuthHeaderOverrideToXAPIKey(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	ep, err := ResolveEndpoint(cfgPath)
 	if err != nil {
@@ -199,7 +205,9 @@ func TestResolveEndpoint_ConfigOpenAIIgnoresAuthHeader(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	ep, err := ResolveEndpoint(cfgPath)
 	if err != nil {
@@ -271,7 +279,9 @@ func TestResolveEndpoint_ProviderAnthropic(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	ep, err := ResolveEndpoint(cfgPath)
 	if err != nil {
@@ -305,7 +315,9 @@ func TestResolveEndpoint_ProviderOpenAI(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	ep, err := ResolveEndpoint(cfgPath)
 	if err != nil {
@@ -334,7 +346,9 @@ func TestResolveEndpoint_ProviderModelOverride(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	ep, err := ResolveEndpoint(cfgPath)
 	if err != nil {
@@ -356,7 +370,9 @@ func TestResolveEndpoint_ProviderEntryModelOverridesDefault(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	ep, err := ResolveEndpoint(cfgPath)
 	if err != nil {
@@ -383,7 +399,9 @@ func TestResolveEndpointWithModelOverride_CustomProviderWithoutConfiguredModel(t
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	ep, err := ResolveEndpointWithModelOverride(cfgPath, "llama-3-8b")
 	if err != nil {
@@ -409,7 +427,9 @@ func TestResolveEndpoint_ProviderAPIKeyEnvFallback(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	ep, err := ResolveEndpoint(cfgPath)
 	if err != nil {
@@ -431,7 +451,9 @@ func TestResolveEndpoint_ProviderMissingAPIKey(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	_, err := ResolveEndpoint(cfgPath)
 	if err == nil {
@@ -448,7 +470,9 @@ func TestResolveEndpoint_ProviderNotConfigured(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	_, err := ResolveEndpoint(cfgPath)
 	if err == nil {
@@ -472,7 +496,9 @@ func TestResolveEndpoint_CustomProvider(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	ep, err := ResolveEndpoint(cfgPath)
 	if err != nil {
@@ -508,7 +534,9 @@ func TestResolveEndpoint_CustomProviderInvalidProtocol(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	_, err := ResolveEndpoint(cfgPath)
 	if err == nil {
@@ -531,7 +559,9 @@ func TestResolveEndpoint_CustomProviderMissingFields(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	_, err := ResolveEndpoint(cfgPath)
 	if err == nil {
@@ -555,7 +585,9 @@ func TestResolveEndpoint_CustomProviderModelFromTopLevel(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	ep, err := ResolveEndpoint(cfgPath)
 	if err != nil {
@@ -578,7 +610,9 @@ func TestResolveEndpoint_LegacyLlmStillWorks(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	ep, err := ResolveEndpoint(cfgPath)
 	if err != nil {
@@ -603,7 +637,9 @@ func TestResolveEndpoint_ProviderAnthropicURLHasMessagesSuffix(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	ep, err := ResolveEndpoint(cfgPath)
 	if err != nil {
@@ -629,7 +665,9 @@ func TestResolveEndpoint_ProviderExtraBody(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	ep, err := ResolveEndpoint(cfgPath)
 	if err != nil {
@@ -654,7 +692,9 @@ func TestResolveEndpointWithModelOverride_ValidModelInPresetList(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	ep, err := ResolveEndpointWithModelOverride(cfgPath, "claude-opus-4-8")
 	if err != nil {
@@ -676,7 +716,9 @@ func TestResolveEndpointWithModelOverride_InvalidModelInPresetList(t *testing.T)
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	_, err := ResolveEndpointWithModelOverride(cfgPath, "claude-opsu-4-6")
 	if err == nil {
@@ -706,7 +748,9 @@ func TestResolveEndpointWithModelOverride_ValidModelInCustomProviderList(t *test
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	ep, err := ResolveEndpointWithModelOverride(cfgPath, "llama-3-8b")
 	if err != nil {
@@ -733,7 +777,9 @@ func TestResolveEndpointWithModelOverride_InvalidModelInCustomProviderList(t *te
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	_, err := ResolveEndpointWithModelOverride(cfgPath, "gpt-4")
 	if err == nil {
@@ -760,7 +806,9 @@ func TestResolveEndpointWithModelOverride_NoValidationWhenNoModelList(t *testing
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	ep, err := ResolveEndpointWithModelOverride(cfgPath, "any-model-name")
 	if err != nil {
@@ -785,7 +833,9 @@ func TestResolveEndpointWithModelOverride_MergesPresetAndEntryModels(t *testing.
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	// Should accept both preset models and entry models.
 	ep1, err := ResolveEndpointWithModelOverride(cfgPath, "claude-opus-4-8")
@@ -823,7 +873,9 @@ func TestResolveEndpointWithModelOverride_LegacyConfigNoValidation(t *testing.T)
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	// Legacy config has no model list, so any override should be accepted.
 	ep, err := ResolveEndpointWithModelOverride(cfgPath, "any-override-model")
@@ -1087,7 +1139,9 @@ func TestResolveEndpoint_ProviderExtraHeaders(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	ep, err := ResolveEndpoint(cfgPath)
 	if err != nil {
@@ -1114,7 +1168,9 @@ func TestResolveEndpoint_LegacyLlmExtraHeaders(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	ep, err := ResolveEndpoint(cfgPath)
 	if err != nil {
@@ -1218,7 +1274,9 @@ func TestResolveEndpoint_ConfigTimeoutSec(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	ep, err := ResolveEndpoint(cfgPath)
 	if err != nil {
@@ -1242,7 +1300,9 @@ func TestResolveEndpoint_NegativeConfigTimeoutSec(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	_, err := ResolveEndpoint(cfgPath)
 	if err == nil {
@@ -1308,7 +1368,9 @@ func TestResolveEndpoint_ProviderConfigTimeoutSec(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	ep, err := ResolveEndpoint(cfgPath)
 	if err != nil {
@@ -1334,7 +1396,9 @@ func TestResolveEndpoint_ProviderConfigNegativeTimeoutSec(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	_, err := ResolveEndpoint(cfgPath)
 	if err == nil {
@@ -1359,7 +1423,9 @@ func TestResolveEndpoint_EnvTimeoutOverridesConfigTimeout(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	ep, err := ResolveEndpoint(cfgPath)
 	if err != nil {
@@ -1387,7 +1453,9 @@ func TestResolveEndpoint_EnvTimeoutOverridesProviderTimeout(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	ep, err := ResolveEndpoint(cfgPath)
 	if err != nil {
@@ -1412,7 +1480,9 @@ func TestResolveEndpoint_InvalidEnvTimeoutWithConfig(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	_, err := ResolveEndpoint(cfgPath)
 	if err == nil {
@@ -1436,7 +1506,9 @@ func TestResolveEndpoint_NegativeEnvTimeoutWithConfig(t *testing.T) {
 	}
 	data, _ := json.Marshal(cfg)
 	cfgPath := filepath.Join(t.TempDir(), "config.json")
-	os.WriteFile(cfgPath, data, 0644)
+	if err := os.WriteFile(cfgPath, data, 0644); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
 
 	_, err := ResolveEndpoint(cfgPath)
 	if err == nil {
diff --git a/internal/mcp/client_test.go b/internal/mcp/client_test.go
index 07aee15..c5f04da 100644
--- a/internal/mcp/client_test.go
+++ b/internal/mcp/client_test.go
@@ -113,7 +113,7 @@ func TestProvider_Execute_Integration(t *testing.T) {
 	}
 
 	c := &Client{name: "test-srv", session: session, tools: toolsResult.Tools}
-	defer c.Close()
+	defer func() { _ = c.Close() }()
 
 	p := &Provider{toolName: "greet", client: c}
 	result, err := p.Execute(ctx, map[string]any{"name": "world"})
@@ -193,7 +193,7 @@ func TestNewClient_Integration(t *testing.T) {
 		session: session,
 		tools:   toolsResult.Tools,
 	}
-	defer c.Close()
+	defer func() { _ = c.Close() }()
 
 	if c.Name() != "test-srv" {
 		t.Errorf("Name() = %q", c.Name())
diff --git a/internal/mcp/stdio_test.go b/internal/mcp/stdio_test.go
index ea9f3d0..b851cad 100644
--- a/internal/mcp/stdio_test.go
+++ b/internal/mcp/stdio_test.go
@@ -68,7 +68,7 @@ func TestNewClient_Stdio(t *testing.T) {
 	if err != nil {
 		t.Fatalf("NewClient: %v", err)
 	}
-	defer c.Close()
+	defer func() { _ = c.Close() }()
 
 	if c.Name() != "test-srv" {
 		t.Errorf("Name() = %q, want %q", c.Name(), "test-srv")
diff --git a/internal/model/model_test.go b/internal/model/model_test.go
index 8da62b8..5ac6273 100644
--- a/internal/model/model_test.go
+++ b/internal/model/model_test.go
@@ -65,14 +65,18 @@ func TestPreviewEntry_ExcludeReasonOmitEmpty(t *testing.T) {
 	}
 	data, _ := json.Marshal(e)
 	var m map[string]any
-	json.Unmarshal(data, &m)
+	if err := json.Unmarshal(data, &m); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
 	if _, ok := m["exclude_reason"]; ok {
 		t.Error("expected exclude_reason to be omitted when empty")
 	}
 
 	e.ExcludeReason = ExcludeUserRule
 	data, _ = json.Marshal(e)
-	json.Unmarshal(data, &m)
+	if err := json.Unmarshal(data, &m); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
 	if m["exclude_reason"] != "user_exclude" {
 		t.Errorf("expected exclude_reason=user_exclude, got %v", m["exclude_reason"])
 	}
diff --git a/internal/pathutil/path_test.go b/internal/pathutil/path_test.go
index 3664e75..ecc4985 100644
--- a/internal/pathutil/path_test.go
+++ b/internal/pathutil/path_test.go
@@ -72,7 +72,7 @@ func TestCanonicalPath_RelativePath(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Getwd: %v", err)
 	}
-	t.Cleanup(func() { os.Chdir(oldWd) })
+	t.Cleanup(func() { _ = os.Chdir(oldWd) })
 	if err := os.Chdir(dir); err != nil {
 		t.Fatalf("Chdir: %v", err)
 	}
diff --git a/internal/session/persist_test.go b/internal/session/persist_test.go
index ddf99c2..6231341 100644
--- a/internal/session/persist_test.go
+++ b/internal/session/persist_test.go
@@ -109,7 +109,7 @@ func readJSONLRecords(t *testing.T, path string) []map[string]any {
 	if err != nil {
 		t.Fatalf("open jsonl: %v", err)
 	}
-	defer f.Close()
+	defer func() { _ = f.Close() }()
 
 	var records []map[string]any
 	scanner := bufio.NewScanner(f)
@@ -165,8 +165,11 @@ func TestSetErrorWritesJSONL(t *testing.T) {
 
 	if sh.persist != nil {
 		sh.persist.mu.Lock()
-		sh.persist.writer.Flush()
+		err := sh.persist.writer.Flush()
 		sh.persist.mu.Unlock()
+		if err != nil {
+			t.Fatalf("flush: %v", err)
+		}
 	}
 
 	path := sessionJSONLPath(t, repoDir, sh.SessionID)
diff --git a/internal/telemetry/config_test.go b/internal/telemetry/config_test.go
index 1e4011a..9a1c215 100644
--- a/internal/telemetry/config_test.go
+++ b/internal/telemetry/config_test.go
@@ -103,7 +103,7 @@ func TestResolveEnv(t *testing.T) {
 			}
 			for _, k := range envKeys {
 				t.Setenv(k, "")
-				os.Unsetenv(k)
+				_ = os.Unsetenv(k)
 			}
 			for k, v := range tc.envs {
 				t.Setenv(k, v)
@@ -128,7 +128,9 @@ func TestLoadFromJSON(t *testing.T) {
 	t.Run("malformed json returns nil error", func(t *testing.T) {
 		tmp := t.TempDir()
 		path := filepath.Join(tmp, "config.json")
-		os.WriteFile(path, []byte("{invalid json"), 0644)
+		if err := os.WriteFile(path, []byte("{invalid json"), 0644); err != nil {
+			t.Fatalf("write file: %v", err)
+		}
 
 		cfg := DefaultConfig()
 		err := LoadFromJSON(&cfg, path)
@@ -140,7 +142,9 @@ func TestLoadFromJSON(t *testing.T) {
 	t.Run("no telemetry section", func(t *testing.T) {
 		tmp := t.TempDir()
 		path := filepath.Join(tmp, "config.json")
-		os.WriteFile(path, []byte(`{"other": "value"}`), 0644)
+		if err := os.WriteFile(path, []byte(`{"other": "value"}`), 0644); err != nil {
+			t.Fatalf("write file: %v", err)
+		}
 
 		cfg := DefaultConfig()
 		err := LoadFromJSON(&cfg, path)
@@ -163,7 +167,9 @@ func TestLoadFromJSON(t *testing.T) {
 				"content_logging": true
 			}
 		}`
-		os.WriteFile(path, []byte(data), 0644)
+		if err := os.WriteFile(path, []byte(data), 0644); err != nil {
+			t.Fatalf("write file: %v", err)
+		}
 
 		cfg := DefaultConfig()
 		err := LoadFromJSON(&cfg, path)
@@ -188,7 +194,9 @@ func TestLoadFromJSON(t *testing.T) {
 		tmp := t.TempDir()
 		path := filepath.Join(tmp, "config.json")
 		data := `{"telemetry": {"otlp_endpoint": "localhost:4317"}}`
-		os.WriteFile(path, []byte(data), 0644)
+		if err := os.WriteFile(path, []byte(data), 0644); err != nil {
+			t.Fatalf("write file: %v", err)
+		}
 
 		cfg := DefaultConfig()
 		err := LoadFromJSON(&cfg, path)
@@ -204,7 +212,9 @@ func TestLoadFromJSON(t *testing.T) {
 		tmp := t.TempDir()
 		path := filepath.Join(tmp, "config.json")
 		data := `{"telemetry": {"exporter": "otlp"}}`
-		os.WriteFile(path, []byte(data), 0644)
+		if err := os.WriteFile(path, []byte(data), 0644); err != nil {
+			t.Fatalf("write file: %v", err)
+		}
 
 		cfg := DefaultConfig()
 		cfg.Exporter = "custom"
@@ -227,7 +237,7 @@ func TestResolveConfig(t *testing.T) {
 		}
 		for _, k := range envKeys {
 			t.Setenv(k, "")
-			os.Unsetenv(k)
+			_ = os.Unsetenv(k)
 		}
 
 		cfg := ResolveConfig("")
@@ -240,7 +250,9 @@ func TestResolveConfig(t *testing.T) {
 		tmp := t.TempDir()
 		path := filepath.Join(tmp, "config.json")
 		data := `{"telemetry": {"enabled": false}}`
-		os.WriteFile(path, []byte(data), 0644)
+		if err := os.WriteFile(path, []byte(data), 0644); err != nil {
+			t.Fatalf("write file: %v", err)
+		}
 
 		t.Setenv("OCR_ENABLE_TELEMETRY", "1")
 
diff --git a/internal/telemetry/events_test.go b/internal/telemetry/events_test.go
index 1bcd170..d9d1efa 100644
--- a/internal/telemetry/events_test.go
+++ b/internal/telemetry/events_test.go
@@ -54,7 +54,7 @@ func captureStderr(t *testing.T, fn func()) string {
 	defer func() { os.Stderr = oldStderr }()
 
 	fn()
-	w.Close()
+	_ = w.Close()
 
 	var buf bytes.Buffer
 	_, _ = io.Copy(&buf, r)
diff --git a/internal/telemetry/exporter_test.go b/internal/telemetry/exporter_test.go
index 1a3c9be..97ebaa2 100644
--- a/internal/telemetry/exporter_test.go
+++ b/internal/telemetry/exporter_test.go
@@ -161,7 +161,9 @@ func TestInitOTLPProviders_ProtocolRouting(t *testing.T) {
 				OTLPProtocol: tc.protocol,
 			}
 			initOTLPProviders(context.Background(), resource.Default(), cfg)
-			w.Close()
+			if err := w.Close(); err != nil {
+				t.Fatalf("close stderr pipe: %v", err)
+			}
 			os.Stderr = oldStderr
 
 			defer func() {
@@ -184,7 +186,9 @@ func TestInitOTLPProviders_ProtocolRouting(t *testing.T) {
 			}
 
 			var buf bytes.Buffer
-			io.Copy(&buf, r)
+			if _, err := io.Copy(&buf, r); err != nil {
+				t.Fatalf("read stderr pipe: %v", err)
+			}
 			stderrOut := buf.String()
 			if tc.wantWarning {
 				if !strings.Contains(stderrOut, "falling back to gRPC") {
diff --git a/internal/telemetry/provider_test.go b/internal/telemetry/provider_test.go
index 3895636..bdbc380 100644
--- a/internal/telemetry/provider_test.go
+++ b/internal/telemetry/provider_test.go
@@ -63,7 +63,7 @@ func TestContentLogging_EnabledWithEnv(t *testing.T) {
 func TestContentLogging_EnabledWithoutEnv(t *testing.T) {
 	setupEnabledTelemetry(t)
 	t.Setenv("OCR_CONTENT_LOGGING", "")
-	os.Unsetenv("OCR_CONTENT_LOGGING")
+	_ = os.Unsetenv("OCR_CONTENT_LOGGING")
 	if ContentLogging() {
 		t.Error("expected ContentLogging()=false when enabled but env var not set")
 	}
@@ -112,7 +112,7 @@ func TestInit_DisabledByDefault(t *testing.T) {
 	}
 	for _, k := range envKeys {
 		t.Setenv(k, "")
-		os.Unsetenv(k)
+		_ = os.Unsetenv(k)
 	}
 
 	defer func() {
@@ -140,7 +140,7 @@ func TestInit_EnabledConsole(t *testing.T) {
 	}
 	for _, k := range envKeys {
 		t.Setenv(k, "")
-		os.Unsetenv(k)
+		_ = os.Unsetenv(k)
 	}
 
 	defer func() {
diff --git a/internal/viewer/handler_test.go b/internal/viewer/handler_test.go
index c7e9179..c24349c 100644
--- a/internal/viewer/handler_test.go
+++ b/internal/viewer/handler_test.go
@@ -82,7 +82,7 @@ func TestHandleRepos_PermissionDenied(t *testing.T) {
 	if err := os.Chmod(root, 0000); err != nil {
 		t.Fatal(err)
 	}
-	t.Cleanup(func() { os.Chmod(root, 0755) })
+	t.Cleanup(func() { _ = os.Chmod(root, 0755) })
 
 	req := httptest.NewRequest("GET", "/", nil)
 	rr := httptest.NewRecorder()
diff --git a/internal/viewer/server_extra_test.go b/internal/viewer/server_extra_test.go
index c4e8b63..04be65d 100644
--- a/internal/viewer/server_extra_test.go
+++ b/internal/viewer/server_extra_test.go
@@ -167,7 +167,7 @@ func TestStaticFS(t *testing.T) {
 	if err != nil {
 		t.Fatalf("failed to open style.css from staticFS: %v", err)
 	}
-	f.Close()
+	_ = f.Close()
 }
 
 func TestResolveAllowedHostsFromEnv(t *testing.T) {
diff --git a/internal/viewer/store_load_test.go b/internal/viewer/store_load_test.go
index 3ed4a92..a4da1db 100644
--- a/internal/viewer/store_load_test.go
+++ b/internal/viewer/store_load_test.go
@@ -405,7 +405,7 @@ func TestDiscoverRepos_SkipsUnreadableSubdir(t *testing.T) {
 	if err := os.Chmod(badRepo, 0000); err != nil {
 		t.Fatal(err)
 	}
-	t.Cleanup(func() { os.Chmod(badRepo, 0755) })
+	t.Cleanup(func() { _ = os.Chmod(badRepo, 0755) })
 
 	repos, err := DiscoverRepos(root)
 	if err != nil {
@@ -439,7 +439,7 @@ func TestListSessions_SkipsUnreadableFiles(t *testing.T) {
 	if err := os.Chmod(badPath, 0000); err != nil {
 		t.Fatal(err)
 	}
-	t.Cleanup(func() { os.Chmod(badPath, 0644) })
+	t.Cleanup(func() { _ = os.Chmod(badPath, 0644) })
 
 	sessions, err := ListSessions(root, "repo")
 	if err != nil {