Engine: lean verification defaults (one reviewer, one fix round, no full-panel re-verify)

[TBarregren]

What to build

Make the engine's verification lean by default:

1. The default verifier panel is a single broad adversarial reviewer (correctness against intent + acceptance criteria, test quality, and any security/data-safety hazard the issue touches). Raise to 2–3 lenses only when the plan marks an issue genuinely high-risk.
2. The default maxFixRounds is 1.
3. On a fix round, re-verify only the findings that were fixed — not the entire panel again.

Why it matters

The combinatorial blow-up — issues x lenses x fix-rounds, each fix round re-running the whole panel, plus a separate integrator, plus worktree isolation — produced roughly 247 sub-agents on a 30-issue run and exhausted the monthly spend limit before anything integrated. Re-running the full panel on every fix round is the single biggest multiplier.

Direction to consider

Change DEFAULT_LENSES to one broad lens; keep per-issue risk-scaling so the plan can still request extra lenses for a genuinely high-risk issue. Default maxFixRounds to 1. After a fix, verify only the fixed findings (or trust the fix and rely on the final integration review) instead of re-dispatching the whole panel.

Acceptance criteria

• The default panel is one adversarial reviewer; extra lenses apply only when the plan marks the issue high-risk.
• maxFixRounds defaults to 1.
• A fix round re-verifies only the fixed findings, not the whole panel.
• For a default (non-high-risk) issue with one finding, the number of verifier agents spawned is demonstrably lower than under the previous defaults.

Blocked by

• Engine: keep feature branches linear and land each green issue incrementally #16

[TBarregren]

Solved on main (82818ea, 403abbf). Default panel is one broad adversarial lens (risk-scaling preserved); maxFixRounds defaults to 1; a fix round re-verifies only the fixed findings via a single targeted agent; a new blockingFindings helper means an issue integrates ONLY when the verifier explicitly cleared (no empty/clear:false silent pass). Test-first, independently reviewed (closed a silent-integration hole), gates green.