feat(libsy-llm-client): Move retry logic from libsy to libsy-llm-client

crates/libsy-llm-client/README.md

@@ -144,9 +144,9 @@ async fn stream(
 ### Routing an algorithm
 
 [`run`] takes a libsy algorithm and a [`ClientRouter`], and returns the final response plus
-the trace of decisions the algorithm published. The router resolves each offloaded call to
-the client for the target the algorithm selected; `ClientRouter::single` is the
-single-provider case:
+the trace of decisions the algorithm published. Each offloaded `CallModel` carries an ordered
+`models` list. The router resolves and tries those candidates in order; `ClientRouter::single`
+is the single-provider case:
 
 ```rust
 use std::sync::Arc;
@@ -249,9 +249,12 @@ fn build_multi_format_client(
   transport failures are retried; streaming body failures are not replayed after
   the response has been returned.
 
-Retries replay the same upstream request. A transport failure can therefore
-duplicate a request that the provider processed but did not finish returning,
-and the retry budget plus capped `Retry-After` delays determines total latency.
+Retries replay the same upstream request to the same model. Each candidate's
+`max_retries` budget is exhausted before candidate fallback advances to the next
+model. The worst case is `candidates × (max_retries + 1)` upstream requests, and
+total latency includes every candidate's capped `Retry-After` backoff. A transport
+failure can duplicate a request that the provider processed but did not finish
+returning.
 
 ## Errors
 

crates/libsy-llm-client/src/observability.rs

@@ -177,7 +177,6 @@ fn client_call_error_type(error: &LibsyError) -> Cow<'static, str> {
         LibsyError::AlgorithmError { .. } => Cow::Borrowed("algorithm_error"),
         LibsyError::Driver(_) => Cow::Borrowed("driver_error"),
         LibsyError::MissingFinalResponse => Cow::Borrowed("missing_final_response"),
-        LibsyError::AllTargetsExcluded => Cow::Borrowed("context_window_exceeded"),
         LibsyError::External { .. } => Cow::Borrowed("_OTHER"),
     }
 }