fix(llm): scope LLM module to where it is actually reachable

The dead-code lint Stefan flagged was a real signal — pretending
otherwise with #[allow(dead_code)] would have hidden a future
genuinely-dead helper. Two structural changes:

1. Gate `mod llm;` in lib.rs to `cfg(any(target_arch = "wasm32",
   test))`. The LLM client only has callers on wasm32 (WakiClient)
   and in the host test harness; on a host non-test build the
   module is genuinely unreachable, so we don't compile it.

2. Add a test that covers every LlmError Display message so the
   `Status` and `MissingInput` variants are constructed in the
   test build (they were used by WakiClient on wasm32 but never
   touched by host tests). The test doubles as a regression net
   for the user-facing error strings.

18 host tests green (was 17). Drops the previous
allow(dead_code) escape hatch entirely.

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

src/lib.rs

@@ -13,6 +13,11 @@
 // ships a fix.
 #![cfg_attr(target_arch = "wasm32", allow(unsafe_op_in_unsafe_fn))]
 
+// The LLM client is only used by the wasm32 production code
+// (WakiClient) and by the host-side test harness. Gating the
+// module declaration keeps the host non-test build honest about
+// what is actually reachable on each target.
+#[cfg(any(target_arch = "wasm32", test))]
 mod llm;
 mod plan;
 

src/llm.rs

@@ -6,12 +6,13 @@
 //! All HTTP I/O lives behind a `LlmClient` trait so unit tests can
 //! exercise the prompt-building and response-parsing logic on the
 //! host without making real network calls.
-
-// On the host build, the LLM functions only have callers in
-// #[cfg(test)] code; the production caller (WakiClient) is
-// wasm32-only. Suppress dead-code warnings for the non-wasm32
-// non-test build that cargo runs as part of --all-targets.
-#![cfg_attr(not(target_arch = "wasm32"), allow(dead_code))]
+//!
+//! This module is only compiled when the production caller
+//! (wasm32) or the host test harness needs it — gated at the
+//! `mod llm;` declaration in `lib.rs`. That way the host
+//! `cargo build --all-targets` does not flag the helpers as
+//! dead code; they genuinely have no host-side caller outside
+//! `#[cfg(test)]`.
 
 use serde::Serialize;
 
@@ -228,6 +229,30 @@ mod tests {
         assert_eq!(messages[1]["content"], "user-text");
     }
 
+    #[test]
+    fn each_error_variant_renders_a_useful_message() {
+        // Documents the expected Display output for every variant
+        // and ensures none drift to silent. Also exercises Status
+        // and MissingInput, which the WakiClient path constructs
+        // but tests do not otherwise reach.
+        assert!(
+            LlmError::MissingInput("llm_model")
+                .to_string()
+                .contains("llm_model")
+        );
+        assert!(
+            LlmError::Http("connection refused".into())
+                .to_string()
+                .contains("connection refused")
+        );
+        assert!(LlmError::Status(503).to_string().contains("503"));
+        assert!(
+            LlmError::Decode("bad json".into())
+                .to_string()
+                .contains("bad json")
+        );
+    }
+
     #[test]
     fn extracts_content_from_well_formed_response() {
         let body =