Per-task `output_schema` (JSON Schema object) on task items plus the
top-level single-goal form — a one-time static addition to the tool
schema (never varies per call).
- Child side: the schema is appended to the child's context as an
explicit OUTPUT CONTRACT block before spawn.
- Completion side: the parent validates the child's final answer with
jsonschema; on failure it sends exactly ONE bounded retry turn
carrying the validation errors verbatim (no schema re-paste).
- Result entries gain schema_valid (+ schema_retries, and schema_errors
on final failure) ONLY when a schema was requested; schema-less calls
keep a byte-identical result shape.
- Malformed schemas are rejected loudly at dispatch (coerce_output_schema
meta-validates via jsonschema's validator_for/check_schema).
- New helpers in tools/delegation_output_schema.py: coerce, contract
block, fence/prose-tolerant extraction+validation, retry message.
Pattern from: github/copilot-cli ctx.agent(prompt,{schema}) — PATTERN
ONLY, zero code/prompt text copied (proprietary); proven consumer:
delegate-task-output-patterns skill.
Tests: tests/tools/test_delegate_output_schema.py (24 tests — valid
first try, invalid->retry->valid, invalid twice -> schema_valid false +
errors surfaced, retry-exception degrade, no-schema legacy shape pin,
dispatch rejection, contract plumbing). Delegation suite: 221/221 green.
Teknium