JSON Schema 2020-12 tool contracts

[g2vinay]

Make tool schemas compatible with the expanded schema model and prepare for richer tool definitions.

Work items:

1. Review current schema generation in the command/tool loader pipeline.
2. Upgrade input-schema generation so it can express composition and references when needed.
3. Add support for output schemas where a tool benefits from structured results.
4. Ensure any validator limits schema depth and execution time.
5. Explicitly block unsafe external $ref dereference behavior.
6. Select a small number of high-value tools as pilots for richer schemas before broad rollout.

Acceptance criteria:

• Existing tools continue to work with the new schema model.
• One or more pilot tools demonstrate richer schema expressiveness.
• Validation remains bounded and safe.