Enable the pstack plugin for cloud agents

[tt-a1i]

Problem

Cloud agents on this repository cannot use pstack skills such as /poteto-mode, /correct, /interrogate, and /benchmark-checklist. Those skills live in Cursor's pstack plugin, and this repo did not enable that plugin.

Value

Future cloud agents on this repo can load pstack through Cursor's project plugin install instead of a copied skill tree. The existing .agents/skills/test-value skill stays the project's own skill.

Approach

Enable pstack through the committed project plugin config that pstack's Benny setup writes for a target repository:

{
  "plugins": {
    "pstack": { "enabled": true }
  }
}

.gitignore ignores every settings.json, including Pi settings. The exception is only .cursor/settings.json, so this plugin config is checked out with the repo.

AGENTS.md records the project rule that overrides pstack's overnight "land even if CI flakes" example: root-cause fixes only, never land through CI flakes, no reruns, no retries, and no wider timeouts.

A copied skill tree was tried and removed. pstack marks those skills disable-model-invocation, and the cloud agent runtime omits that class from request context unless the skill has plugin identity. A fresh cloud agent also did not list newly added .agents/skills or .cursor/skills entries; the only project skill in its catalog was test-value, which is already on main.

Validation

• .cursor/settings.json is tracked. git diff origin/main is only this file, .gitignore, and AGENTS.md.
• Cloud agent bc-ee0fa347-48b8-5eb4-8078-9530eca175cc, started from the settings-only commit 7a1b4d3, checked out .cursor/settings.json with plugins.pstack.enabled: true. ~/.cursor/plugins was absent, and its skill catalog did not include poteto-mode, correct, interrogate, or benchmark-checklist.
• Cloud agent bc-a8adbee5-72df-59c7-8bbe-3e960716abd6, started from commit e1a7447 with pstack 0.15.25 copied under .cursor/skills, had those SKILL.md files on disk (54 skills, including the four named above) and .cursor/agents/poteto-agent.md. Its catalog still listed only /workspace/.agents/skills/test-value/SKILL.md among project skills (31 skills total).
• Cloud agent bc-4494e1ab-bd49-5428-b9ab-7321b8337dfe, started from commit 3b1de24, also did not list .agents/skills/setup-pstack/SKILL.md (no disable-model-invocation) or .agents/skills/correct/SKILL.md. Those copies were removed after that check.

Impact

• User-visible behavior: none in OpenPI.
• Model-visible context: AGENTS.md now forbids landing through CI flakes. pstack skills are expected once Cursor provisions the project plugin; this branch does not vendor them.
• Runtime/lifecycle: none.
• Persisted config/data: project Cursor plugin enablement only.
• Compatibility or risk: Pi settings.json remains ignored. pstack's overnight flake example does not apply here. A cloud agent started from this branch did not receive a plugin cache, so plugin provisioning is not demonstrated until a cloud agent is started with this commit as the repository revision Cursor indexes.