[ScriptedAlchemy]

Problem

pstack resolved exact delegation targets using installation and authentication checks, but did not apply delegation's cooldown and project-aware pool checks. An agent could receive a cooling account or an exhausted pool as its exact target and then have delegate_task reject it.

Changes

• Use the existing delegationProviderConstraints predicate for both default role selection and explicit targets.
• Supply the current settings, project ID, provider snapshots, and one Effect clock timestamp from PstackPack.expandComposer.
• Default roles skip unavailable instances and choose an eligible alternative. Explicit unavailable targets retain the existing parent-model fallback and include the reason.
• Keep a pool usable when at least one member is healthy and enabled for the project.

This is the remaining pstack availability follow-up to the integration audit. It targets main independently of #19.

Validation

• Added service regressions for default selection skipping a cooling instance, explicit cooling targets, exhausted pools, a pool whose only healthy member is disabled for the project, and a pool with a healthy eligible member.
• Before the fix: four regressions failed and the healthy-pool control passed.
• After the fix: vp run check:changed --serial passed the native project-memory build, formatting, lint, both knip passes, GraphQL generation check, typechecks for three affected packages, and 95 tests across three files.
• The existing MCP regression still dispatches pstack Opus and Astra targets identically under Claude and Codex parents.
• Independent source review and git diff --check passed.

Runtime check through PstackPack.expandComposer with fixture providers:

Default with cooling and ready instances:
- architect runners: [1] {"providerInstanceId":"claudeAgent_ready","model":"claude-opus-5-5","options":[{"id":"effort","value":"xhigh"},{"id":"fastMode","value":false}]} [2] inherit
Explicit cooling target:
- architect runners: [1] inherit
- Fallback: architect runners seat 1 claudeAgent/claude-opus-5-5 unavailable (Provider is rate limited. Retry after its cooldown expires.); runs on the parent model.

Delegation continues to recheck availability at dispatch, since quota can change after prompt expansion. Full-suite and build validation remain with CI.

Implemented and verified with GPT-6 Astra Pro in the Codex harness.

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