Model Groups spawn router

[grzegorznowak]

Summary

Implements the Model Groups spawn-router story end to end: operators can define named model groups, get prompt/autocomplete guidance for them, and route spawned child agents through a group while the default inherited spawn path remains unchanged.

What changed

• Added Model Groups persistence/state and TUI flows for global/project groups, validation, effective group resolution, and project-over-global overrides.
• Added #group-name autocomplete for effective groups; suggestions show compact provider/model/thinking details for the operator while inserting only prompt text.
• Refreshed system prompt guidance with names-only group availability and confidence/fallback rules; provider/model/auth/persistence details are not exposed in the prompt.
• Extended spawn with optional exact group routing and stopped advertising thinking; stale cached thinking arguments are accepted but ignored.
• Routed spawn calls randomly choose one available authenticated member from the requested group per call. Empty groups or groups with no usable authenticated entries fail clearly; unknown groups fall back to parent model/thinking.
• Routed child thinking uses the selected entry's configured thinking level when present, otherwise inherits parent thinking, then clamps to the selected model capability.
• Child sessions prefer the parent runtime registry/auth while keeping session manager, messages, tools, and spawn isolation intact.
• Spawn result rendering now distinguishes inherited default routing, successful group routing, and unknown-group fallback identity.

Out of scope

• Interactive picker/chooser at spawn time.
• Automatic routing without explicit operator group intent.
• Registering groups as model picker entries or meta-model proxies.
• Child profiles, frontmatter, extra tools, budget/context policies, weighted/priority/health/rate-limit routing, retry-time group failover, fuzzy matching, or explicit provider/model override params on spawn.

Verification

• npm test passed (190/190).
• npm run test:e2e passed (10/10).
• npx tsc --noEmit passed.
• npm audit --omit=dev --audit-level=moderate passed.
• Latest PR CI for 6733bfd succeeded: https://github.com/agenticoding/pi-agenticoding/actions/runs/27600878769

CI note / follow-up

• The latest fix isolates Windows test homes by setting HOME, USERPROFILE, HOMEDRIVE, and HOMEPATH for model-groups tests.
• CI now runs a runtime dependency audit with --omit=dev. The full dev audit is still blocked by upstream shrinkwrapped Pi dev dependencies, so this PR does not claim the upstream Pi audit issue is fixed. Restore strict full-dev audit after the upstream fix is released and the lockfile is updated.

References

• Initiative: model-tag-router
• Story: model-groups-spawn-router — Model Groups spawn router