fix: address Copilot review feedback

1. Cache key now includes provider+model name to prevent stale vector
   reuse when switching embedding providers (would cause NaN scores)
2. Error hint in semantic-navigate references embed model instead of
   chat model for embedding failures

Author: Cenk Tekin

src/core/embeddings.ts

@@ -80,7 +80,8 @@ const OPENAI_EMBED_MODEL = process.env.CONTEXTPLUS_OPENAI_EMBED_MODEL ?? process
 const OPENAI_API_KEY = process.env.CONTEXTPLUS_OPENAI_API_KEY ?? process.env.OPENAI_API_KEY ?? "";
 const OPENAI_BASE_URL = process.env.CONTEXTPLUS_OPENAI_BASE_URL ?? process.env.OPENAI_BASE_URL ?? "https://api.openai.com/v1";
 const CACHE_DIR = ".mcp_data";
-const CACHE_FILE = "embeddings-cache.json";
+const ACTIVE_EMBED_MODEL = EMBED_PROVIDER === "openai" ? OPENAI_EMBED_MODEL : EMBED_MODEL;
+const CACHE_FILE = `embeddings-cache-${EMBED_PROVIDER}-${ACTIVE_EMBED_MODEL.replace(/[^a-zA-Z0-9._-]/g, "_")}.json`;
 const MIN_EMBED_BATCH_SIZE = 5;
 const MAX_EMBED_BATCH_SIZE = 10;
 const DEFAULT_EMBED_BATCH_SIZE = 8;

src/tools/semantic-navigate.ts

@@ -29,6 +29,7 @@ interface ClusterNode {
 }
 
 const EMBED_PROVIDER = (process.env.CONTEXTPLUS_EMBED_PROVIDER ?? "ollama").toLowerCase();
+const EMBED_MODEL = process.env.OLLAMA_EMBED_MODEL ?? "nomic-embed-text";
 const CHAT_MODEL = process.env.OLLAMA_CHAT_MODEL ?? "llama3.2";
 const OPENAI_CHAT_MODEL = process.env.CONTEXTPLUS_OPENAI_CHAT_MODEL ?? process.env.OPENAI_CHAT_MODEL ?? "gpt-4o-mini";
 const OPENAI_API_KEY = process.env.CONTEXTPLUS_OPENAI_API_KEY ?? process.env.OPENAI_API_KEY ?? "";
@@ -294,7 +295,7 @@ export async function semanticNavigate(options: SemanticNavigateOptions): Promis
   } catch (err) {
     const providerHint = EMBED_PROVIDER === "openai"
       ? `Check CONTEXTPLUS_OPENAI_API_KEY and CONTEXTPLUS_OPENAI_BASE_URL.`
-      : `Make sure Ollama is running with model ${CHAT_MODEL}.`;
+      : `Make sure Ollama is running (check OLLAMA_HOST) and that the embedding model configured in OLLAMA_EMBED_MODEL is available.`;
     return `Embedding provider (${EMBED_PROVIDER}) not available: ${err instanceof Error ? err.message : String(err)}\n${providerHint}`;
   }