Harden MCP server guard and log formatting against secondary crashes

Message

Wrap format-exception and log-error in the tool call guard with their own guards so a failure in error formatting or logging cannot escape and crash the server. Make format-text-field in sigil-log defensive against non-keyword field keys instead of crashing with keyword->string.

Changed

 src/sigil/log.sgl | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Diff

src/sigil/log.sglmodified

@@ -202,7 +202,10 @@

202

203

;; Format a keyword-value pair for text output.

204

(define (format-text-field pair)

−205

(let ((key (keyword->string (car pair)))

+205

(let ((key (if (keyword? (car pair))

+206

(keyword->string (car pair))

+207

(call-with-output-string

+208

(lambda (p) (write (car pair) p)))))

209

(val (cdr pair)))

210

(string-append key "=" (if (string? val)

211

val