Make GPT-6.1 Sol the Sol default and admit the ultra effort

[ericlitman]

Goal

Make codex:gpt-6.1-sol the Sol family default, replacing gpt-5.6-sol. Admit the ultra effort for any model whose Codex CLI entry lists it.

Context

• Codex CLI 0.159.3's model list includes gpt-6.1-sol with efforts low, medium, high, xhigh, max, and ultra. gpt-6-luna and gpt-5.6-luna do not list ultra.
• The model matrix at plugins/pstack/skills/poteto-mode/references/provider-dispatch.md:11-18 already gives each row its own selectable efforts, but the prose fixes the effort universe at low through max.
• Sol is the default for the bug-fix, perf-issue, and hillclimb roles, and it sits in the arena, architect, and interrogate panels. The slug gpt-5.6-sol is copied into 11 upstream-derived skill files, which tests/skill-collision-repro.sh keeps in sync.
• Decided by the maintainer on 2026-10-01 during triage (docs/plans/2026-10-01-triage-and-roadmap.md). Related: Support GPT-6 Sol, GPT-6 Luna, and an exact Opus 5.5 pstack pin #85 (optional GPT-6 Sol and Luna, exact Opus 5.5 pin), the closed PR feat(models): move Sol to gpt-6-sol and Grok to grok-4.7 #83 (Sol moved to gpt-6-sol).

Acceptance criteria

• The Sol row's model is gpt-6.1-sol, and every role or panel default that names Sol uses codex:gpt-6.1-sol@max.
• The effort universe includes ultra. A row offers ultra only when its CLI model entry lists it. Setup rejects ultra for a model that does not list it.
• The runner passes ultra through unchanged, and the tests cover it.
• An existing sheet that says codex:gpt-5.6-sol@<effort> keeps running until setup asks to replace it. Setup proposes gpt-6.1-sol on rerun.
• CHANGES.md records the default change. UPSTREAM.md keeps the existing exclusion that keeps bug-fix, perf-issue, and hillclimb on Sol.
• Bun tests, strict typecheck, static invariants, and plugin validation pass.
• Live: on the installed candidate, a native Codex probe at gpt-6.1-sol@max and @ultra and an external Codex probe from a Claude Code parent each return a receipt or transcript that names gpt-6.1-sol.