Preserve complete agent-task workflow JSON outputs

[chubes4]

Summary

Prevent GitHub workflow outputs from silently truncating structured JSON.

What changed

• Validate projection byte limits, emit typed artifact-relative references for oversized system outputs, and fail oversized user projections before success.

How to test

1. Run npm run build; expect TypeScript packages compile..
2. Run npm run test:agent-task-contracts; expect Agent-task workflow contract tests pass..

Compatibility

Small outputs are unchanged; oversized system outputs become typed references and oversized declared projections now fail explicitly.

Evidence

• Base unchanged since verification: main remains at 95417fb.
• Reviewer-resolvable source evidence: Reject oversized structured workflow outputs instead of truncating JSON #1832
• Verified finalization base: main at 95417fb
• agent-task-contracts: Passed
• build: Passed

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode general subagent
• Model: openai/gpt-5.6-sol
• Used for: Implemented bounded structured outputs, typed artifact references, and boundary tests; Chris reviews and owns the change.

Source relationships

• Closes Reject oversized structured workflow outputs instead of truncating JSON #1832