feat: Report Truncated Output Artifacts

api/README.md

@@ -94,6 +94,17 @@ Other package-format-compatible runtimes (Go, Rust, Java, GCC) can be installed
 
 Execute code in a sandboxed environment.
 
+When supported output files are omitted because the response reaches its file
+count limit, nesting or path limits, file-size limit, or a filesystem entry
+cannot be read, the response includes `artifact_truncation`. Its `reasons`
+object counts detected omissions by cause, `skipped_count` reports the total
+detected omissions, and `skipped` contains up to 20 relative paths so callers
+can match an expected output. Intentional filters such as unsupported file
+extensions, hidden runtime directories, and unchanged session files do not
+produce this marker when they can be classified within the bounded scan. A
+depth-capped subtree that exceeds the metadata probe budget is reported
+conservatively rather than allowing post-execution traversal to run unbounded.
+
 ### `GET /api/v2/runtimes`
 
 List available language runtimes.