fix(no-hephaestus-non-gpt): add opt-out for model enforcement

[code-yeongyu]

Summary

• Add agents.hephaestus.allow_non_gpt_model schema support (default behavior unchanged when unset/false).
• Update no-hephaestus-non-gpt hook to honor this option: still show toast, but only force-switch to Sisyphus when opt-out is disabled.
• Add hook test coverage for opt-out mode to verify warning toast and no forced agent switch.

Testing

• bun test src/hooks/no-hephaestus-non-gpt/
• bun run typecheck

Fixes #2054

---

Summary by cubic

Adds an opt‑out so Hephaestus can run with non‑GPT models without forcing a switch, and updates provider gating so Hephaestus is not created when only GitHub Copilot is connected. Fixes #2054.

• New Features

  • Schema: agents.hephaestus.allow_non_gpt_model (optional boolean).
  • Hook: honors the setting. Unset/false → error toast and switch to Sisyphus. True → warning toast only, no switch.
  • Wiring/tests: passes the setting from plugin config and adds coverage for the opt‑out path.

• Bug Fixes

  • Provider gating: revert adding github-copilot to Hephaestus requiresProvider; update tests to expect Hephaestus is not created with Copilot-only and mock cache to fix flakiness.

^{Written for commit 9f64e2a. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 4 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

_{Auto-approved: Additive change with a new optional configuration flag. Logic defaults to existing behavior when the flag is unset. Verified by new tests and zero detected issues by cubic.}

[cubic-dev-ai]

2 issues found across 2 files (changes from recent commits).

Prompt for AI agents (all issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="src/shared/model-requirements.ts">

<violation number="1">
P1: This line removes `github-copilot` from `requiresProvider`, which contradicts the PR description stating it should be added.</violation>

<violation number="2">
P1: This line removes `github-copilot` from the providers list, which contradicts the PR description stating it should be added.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}