fix(ik-llama-cpp): adapt to common_grammar struct in sampling.h (#9512)

Upstream ik_llama.cpp commit e0596bf6 ("Autoparser") changed
common_params_sampling::grammar from std::string to a common_grammar
struct (type + grammar), which broke our two direct accesses:

 - JSON ingest fed the field through json_value<common_grammar>(...),
   for which nlohmann has no from_json adapter.
 - JSON export emitted the struct directly, for which nlohmann has no
   to_json adapter.

Wrap the incoming JSON string in common_grammar{COMMON_GRAMMAR_TYPE_USER, ...}
and serialize via the inner .grammar member, mirroring upstream's
examples/server/server-context.cpp.

Also bump IK_LLAMA_VERSION to 286ce324baed17c95faec77792eaa6bdb1c7a5f5
so the local-ai side lines up with the dependency bump in #9496.

Assisted-by: Claude-Code:claude-opus-4-7

Author: mudler

backend/cpp/ik-llama-cpp/Makefile

@@ -1,5 +1,5 @@
 
-IK_LLAMA_VERSION?=d4824131580b94ffa7b0e91c955e2b237c2fe16e
+IK_LLAMA_VERSION?=286ce324baed17c95faec77792eaa6bdb1c7a5f5
 LLAMA_REPO?=https://github.com/ikawrakow/ik_llama.cpp
 
 CMAKE_ARGS?=

backend/cpp/ik-llama-cpp/grpc-server.cpp

@@ -686,7 +686,16 @@ struct llama_server_context
         slot->sparams.mirostat_eta      = json_value(data, "mirostat_eta",      default_sparams.mirostat_eta);
         slot->params.n_keep             = json_value(data, "n_keep",            slot->params.n_keep);
         slot->sparams.seed               = json_value(data, "seed",              default_sparams.seed);
-        slot->sparams.grammar           = json_value(data, "grammar",           default_sparams.grammar);
+        {
+            // upstream changed common_params_sampling::grammar from std::string to
+            // the common_grammar struct (type + grammar). The incoming JSON still
+            // carries a plain string, so build the user-provided grammar here and
+            // fall back to the server default when the request omits it.
+            std::string grammar_str = json_value(data, "grammar", std::string());
+            slot->sparams.grammar = grammar_str.empty()
+                ? default_sparams.grammar
+                : common_grammar{COMMON_GRAMMAR_TYPE_USER, std::move(grammar_str)};
+        }
         slot->sparams.n_probs           = json_value(data, "n_probs",           default_sparams.n_probs);
         slot->sparams.min_keep          = json_value(data, "min_keep",          default_sparams.min_keep);
         slot->sparams.grammar_triggers = grammar_triggers;
@@ -1232,7 +1241,7 @@ struct llama_server_context
              //      {"logit_bias",        slot.sparams.logit_bias},
             {"n_probs",           slot.sparams.n_probs},
             {"min_keep",          slot.sparams.min_keep},
-            {"grammar",           slot.sparams.grammar},
+            {"grammar",           slot.sparams.grammar.grammar},
             {"samplers",          samplers}
         };
     }