fix(exec): strip trailing result-schema JSON from local model output

Small models (phi4-mini) produce correct markdown analysis but then
append the old {status/phase/skill} JSON schema out of training habit.
stripResultJSON() detects and removes these trailing fences so Claude
Code receives clean prose regardless of model behaviour.

Non-schema json blocks (config examples etc) are preserved.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/exec/litellm_test.go

@@ -80,6 +80,40 @@ func TestLiteLLMErrorOnEmptyChoices(t *testing.T) {
 	assert.ErrorContains(t, err, "no choices")
 }
 
+func TestLiteLLMStripsTrailingResultJSON(t *testing.T) {
+	content := "## Hypotheses\n\n**H1 (high):** nil map access.\n\n```json\n{\n  \"status\": \"pass\",\n  \"phase\": \"debug\",\n  \"skill\": \"debug\"\n}\n```"
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusOK)
+		_, _ = w.Write(chatResponse(t, content))
+	}))
+	defer srv.Close()
+
+	ex := iexec.NewLiteLLM(srv.URL, "", 5*time.Second)
+	text, _, err := ex.Complete(context.Background(), "model", "sys", "user")
+	require.NoError(t, err)
+	assert.Contains(t, text, "nil map access")
+	assert.NotContains(t, text, `"status"`)
+	assert.NotContains(t, text, "```json")
+}
+
+func TestLiteLLMKeepsNonResultJSONFence(t *testing.T) {
+	// A json block that is part of the actual answer (no status/phase) should be kept.
+	content := "Use this config:\n\n```json\n{\"model\": \"koala/phi4\"}\n```"
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusOK)
+		_, _ = w.Write(chatResponse(t, content))
+	}))
+	defer srv.Close()
+
+	ex := iexec.NewLiteLLM(srv.URL, "", 5*time.Second)
+	text, _, err := ex.Complete(context.Background(), "model", "sys", "user")
+	require.NoError(t, err)
+	assert.Contains(t, text, `"model"`)
+	assert.Contains(t, text, "```json")
+}
+
 func TestLiteLLMRespectsContextCancellation(t *testing.T) {
 	ctx, cancel := context.WithCancel(context.Background())
 	cancel()