fix: clear Ollama-unreachable error naming the endpoint + fix hint

Signed-off-by: flemming-it <sf@flemming.it>

src/lib.rs

@@ -44,7 +44,7 @@ pub fn invoke(_ctx: Context, inputs: Inputs) -> Result<Outputs, ModuleError> {
         prompt: &prompt,
     };
     let result = crate::llm::chat_with_identity(&client, &params)
-        .map_err(|e| ModuleError::internal(e.to_string()))?;
+        .map_err(|e| llm_error_to_module_error(e, &endpoint, &model))?;
 
     Ok(Outputs::new()
         .with_text("translation", result.response)
@@ -55,6 +55,32 @@ pub fn invoke(_ctx: Context, inputs: Inputs) -> Result<Outputs, ModuleError> {
         .with_text("model_digest", result.model_digest.unwrap_or_default()))
 }
 
+/// Turn a transport/protocol error into a message that names the
+/// likely cause and the fix, instead of a raw `ConnectionRefused`.
+fn llm_error_to_module_error(e: crate::llm::LlmError, endpoint: &str, model: &str) -> ModuleError {
+    use crate::llm::LlmError;
+    match e {
+        LlmError::Http(detail) => ModuleError::internal(format!(
+            "LLM endpoint {endpoint} not reachable ({detail}). Is Ollama running? \
+             Start it with `ollama serve`, then pull the model with `ollama pull {model}`. \
+             If the LLM runs elsewhere, set the `endpoint` input to its /api URL."
+        )),
+        LlmError::Status(404) => ModuleError::internal(format!(
+            "LLM endpoint {endpoint} returned 404 for model '{model}' — the model is \
+             likely not pulled. Run `ollama pull {model}` (or check the model name)."
+        )),
+        LlmError::Status(code) => ModuleError::internal(format!(
+            "LLM endpoint {endpoint} returned HTTP {code} for model '{model}'."
+        )),
+        LlmError::Decode(detail) => ModuleError::internal(format!(
+            "LLM response from {endpoint} was not valid Ollama JSON: {detail}"
+        )),
+        LlmError::MissingInput(name) => {
+            ModuleError::invalid_input(format!("missing required input '{name}'"))
+        }
+    }
+}
+
 fn build_prompt(source: &str, target: &str, text: &str) -> String {
     if source.is_empty() {
         format!(