fix(agentic-engineering): validate ad hoc gh JSON fields at the Surveyor call site

[devantler]

🤖 Generated by the Agent Improver

Observed failure

The consumer-wide H59 rule intended to stop cross-subcommand gh --json field reuse, but the post-intervention target moved in the wrong direction: 11 genuine Unknown JSON field failures across 3 Claude sessions in the latest 24-hour window, versus the 1-per-46-session baseline. All 11 failures were Surveyor reads that requested an unsupported field from gh run list; none was prose, a negative control, or documentation.

The portable Surveyor entrypoint does not carry the exact-subcommand vocabulary preflight, so the consumer rule is too far from the caller. A rejected field list aborts the whole request and can be misread as an empty result.

Proposed repair

• Put the preflight in the portable portfolio-surveyor Safety contract.
• For prescribed reads, keep the reviewed literal field list.
• Before any ad hoc JSON read, discover fields from that same subcommand with bare --json, validate every requested field, and never transfer field names across subcommands.
• Treat a failed vocabulary probe or validated read as QUERY-UNKNOWN, never as an empty result.
• Add a focused contract test and bump the agentic-engineering plugin cache key.

Acceptance

• RED proves the current entrypoint lacks the call-site contract.
• GREEN and ablation prove all four clauses are required.
• Plugin validation, manifest parity, version-bump, and script tests pass.
• The next hypothesis measures the exact error signature after rollout; safety and cross-lane coordination remain QUERY-UNKNOWN until independently measurable.

Upstream repair for devantler-tech/monorepo#3049.