configurable path for MCP/RAG

scripts/mcp-http-howto.md

@@ -147,6 +147,11 @@ Query parameters:
 curl "http://127.0.0.1:48888/mcp/rag/query?text=Explain%20differential%20rectification&topK=5"
 ```
 
+RAG root path (optional, for non-standard checkouts):
+```
+-Delphel.rag.root=/home/elphel/wksp2/imagej-elphel
+```
+
 Example (config directory):
 ```
 -Delphel.mcp.allowed.configdir=/media/elphel/btrfs-data/lwir16-proc/NC/config

src/main/java/com/elphel/imagej/mcp/McpServer.java

@@ -552,8 +552,12 @@ public class McpServer {
             if (topK < 1) {
                 topK = 1;
             }
-            String venvPython = "/home/elphel/git/imagej-elphel/attic/CODEX/rag_index/.venv/bin/python";
-            String script = "/home/elphel/git/imagej-elphel/scripts/rag_query.py";
+            String ragRoot = System.getProperty("elphel.rag.root");
+            if (ragRoot == null || ragRoot.trim().isEmpty()) {
+                ragRoot = "/home/elphel/git/imagej-elphel";
+            }
+            String venvPython = ragRoot + "/attic/CODEX/rag_index/.venv/bin/python";
+            String script = ragRoot + "/scripts/rag_query.py";
             List<String> cmd = new ArrayList<String>();
             cmd.add(venvPython);
             cmd.add(script);
@@ -567,7 +571,8 @@ public class McpServer {
             try {
                 p = pb.start();
             } catch (IOException e) {
-                sendJson(exchange, 500, "{\"ok\":false,\"error\":\"Failed to start rag_query\"}");
+                String detail = jsonEscape("rag_root=" + ragRoot + " venv=" + venvPython + " script=" + script + " err=" + e.getMessage());
+                sendJson(exchange, 500, "{\"ok\":false,\"error\":\"Failed to start rag_query\",\"detail\":\"" + detail + "\"}");
                 return;
             }
             byte[] out;