fix: prevent validation errors from triggering MCP error callbacks

Previously, the tool system conflated two distinct types of errors:
1. Processing/validation errors (expected, normal flow)
2. Tool execution failures (unexpected, exceptional)

Both types were being passed to the MCP callback's error parameter,
causing validation failures to be treated as infrastructure errors
at the MCP protocol level.

This change ensures only actual exceptions trigger MCP error callbacks
by:
- Always passing 'false' for the error parameter in normal flow
- Maintaining exception handling for true tool failures
- Preserving validation errors in the result for proper handling

The commented-out original code (:error formatted) is retained for
reference, with extensive inline documentation explaining the
distinction between these error types and suggesting a future
enhancement to introduce :exception-error for clearer separation.

This aligns with error handling best practices where business logic
errors (validation, processing) are distinguished from system failures
(exceptions, infrastructure issues), ensuring the MCP protocol layer
only receives error signals for genuine tool malfunctions.

Author: Bruce Hauman

src/clojure_mcp/tool_system.clj

@@ -96,7 +96,17 @@
                       validated (validate-inputs tool-config keywordized-params)
                       result (execute-tool tool-config validated)
                       formatted (format-results tool-config result)]
-                  (callback (:result formatted) (:error formatted)))
+                  ;; signaling an error to the MCP server should only
+                  ;; happen on tool failure IE an exception.
+                  ;; currently our internal errors conflate processing
+                  ;; errors that occur as a matter of course with
+                  ;; errors in the tools function we need to treat
+                  ;; the (:error formatted) as errors that occur from
+                  ;; the MCP sending bad data vs a new level of
+                  ;; error (:exception-error formatted) [This dosn't exist yet]
+                  ;; which should indicate the the tool isn't functioning correctly.
+
+                  (callback (:result formatted) false #_(:error formatted)))
                 (catch Exception e
                   (log/error e)
                   ;; On error, create a sequence of error messages