feat(cmind): add Codex support and multi-agent backend switchingFeat/codermind codex support

[HYS (HuYaSen)]

Summary

Add Codex CLI as a supported CoderMind runtime while preserving the existing Claude Code and GitHub Copilot integrations.

CoderMind now provisions Claude, Copilot, and Codex together while allowing the active encoder/decoder backend to be switched independently through .cmind/config.toml.

Key changes

• Add a Codex runtime adapter based on codex exec.
• Generate project-scoped Codex skills under .agents/skills/.
• Register rpg-tools safely in .codex/config.toml.
• Add backend switching for copilot, claude, and codex.
• Provision all supported agent integrations regardless of the active backend.
• Isolate per-agent MCP configuration failures so one client cannot block the others.
• Add the standard MCP resource rpg://tree while retaining all existing MCP tools.
• Reload MCP graph state when rpg.json changes.

Reliability improvements

• Make forced planning bypass stale checkpoints consistently.
• Require complete data-flow type coverage during base-class generation.
• Resolve qualified interface edges during call-graph validation.
• Persist RPG Edit code and review results for reliable resume behavior.
• Harden code-generation retries and branch naming.
• Recover corrupted RPG data through the central loader.
• Preserve dependency-graph file stems.
• Keep Codex sandbox bypass as an explicit opt-in for trusted automation.

Compatibility

Shared planning, encoding, code generation, MCP, and RPG Edit paths remain backend-neutral.

• GitHub Copilot continues to use the existing MCP tools.
• Claude Code retains its command and MCP configuration.
• Codex uses project skills and the MCP resource compatibility path.
• User-owned MCP configuration is preserved.
• A configuration conflict for one agent no longer prevents other agents from being configured.

Validation

• CoderMind suite: 1526 passed
• cmbench suite: 243 passed
• Codex Encoder E2E: PASS
  • full encode
  • MCP access
  • CRUD hooks
  • RPG Edit and final synchronization
• Codex Decoder E2E: PASS
  • 48/48 code-generation tasks
  • 178 final tests passed
  • repository and RPG heads synchronized
• Live GitHub Copilot CLI MCP smoke: PASS
  • invoked list_rpg_tree
  • recorded client_context=copilot-agent
• git diff --check: PASS