ci: install pnpm 11.12 directly with npm

[rjan90]

Summary

• install the regular Node-based pnpm 11.12.0 package directly with npm
• assert that the active pnpm version is exactly 11.12.0
• bypass both broken pnpm/action-setup self-update paths

Why

The stability job in run 29227598125 started the devnet successfully, then failed before scenario execution while pnpm/action-setup@v6 tried to self-update its pnpm 11.7.0 bootstrap to 11.12.0.

The initial standalone workaround also proved unsuitable: pnpm setup completed, but the published @pnpm/exe 11.12.0 platform package lacked its executable, causing scenario pnpm installs to fail with @pnpm/exe/pnpm: 1: This: not found.

Node.js 24 is already configured earlier in the workflow, so installing the regular pnpm@11.12.0 npm package avoids both upstream failures while keeping CI on the current release.

Upstream references:

• pnpm self-update issue
• pending self-update fix
• incomplete 11.12.0 standalone packages

Fixes #149.
Fixes #150.

Impact

Nightly stability and frontier jobs can proceed through pnpm setup and execute scenarios with pnpm 11.12.0. The version remains explicit, so future releases do not alter CI without review.

Validation

• workflow YAML parses successfully
• regular pnpm@11.12.0 package reports version 11.12.0
• PR CI run 29231938057 passed:
  • lint: passed
  • cargo tests: passed
  • devnet scenario job: passed
  • scenarios: 5 passed, 0 failed
  • storage E2E and caching subsystem both passed

[rvagg]

this will need to be undone .. can you open an issue in the repo for it too please so we don't lose track?

[rjan90]

this will need to be undone .. can you open an issue in the repo for it too please so we don't lose track?

I opened it here: #152