[Bug]: Fallback chains silently skip github-copilot — model IDs don't match copilot's catalog

[mrm007]

Prerequisites

• I will write this issue in English (see our Language Policy)
• I have searched existing issues to avoid duplicates
• I am using the latest version of oh-my-opencode
• I have read the documentation

Bug Description

Fallback chains in model-requirements.ts include github-copilot as a provider, but the model IDs used don't match what GitHub Copilot actually serves. This causes the resolution to silently skip copilot and fall through to lower-quality free models.

Example — sisyphus fallback chain:

{ providers: ["anthropic", "github-copilot", "opencode"], model: "claude-opus-4-6", variant: "max" },
{ providers: ["kimi-for-coding"], model: "k2p5" },
{ providers: ["opencode"], model: "kimi-k2.5-free" },
{ providers: ["zai-coding-plan"], model: "glm-4.7" },
{ providers: ["opencode"], model: "glm-4.7-free" },  // ← lands here

The chain references claude-opus-4-6 but copilot serves it as claude-opus-4.6 (dot, not hyphen). The model resolution can't match, skips github-copilot, and falls all the way to glm-4.7-free.

Copilot model catalog (from opencode models):

github-copilot/claude-haiku-4.5
github-copilot/claude-opus-4.5
github-copilot/claude-opus-4.6
github-copilot/claude-opus-41
github-copilot/claude-sonnet-4
github-copilot/claude-sonnet-4.5

Fallback chain model IDs:

claude-opus-4-6    → copilot has claude-opus-4.6 (dot)
claude-sonnet-4-5  → copilot has claude-sonnet-4.5 (dot)
claude-haiku-4-5   → copilot has claude-haiku-4.5 (dot)

Steps to Reproduce

1. Connect only github-copilot (no anthropic provider)
2. Start a session — sisyphus should use github-copilot/claude-opus-4-6 per fallback chain
3. Observe it falls through to glm-4.7-free instead

Expected Behavior

When anthropic is unavailable, the fallback chain should resolve to github-copilot/claude-opus-4.6 (or whatever the correct copilot model ID is).

Actual Behavior

Model resolution silently skips github-copilot due to ID mismatch and falls through to much lower-quality free models.

Impact

This affects every fallback chain that lists github-copilot alongside anthropic Claude models — which is most agents and categories. Users who rely on copilot (e.g. Copilot Pro+ subscribers without an Anthropic API key) silently get degraded model quality with no indication of why.

Suggested Fix

Either:

1. Normalize model IDs during resolution (treat hyphens and dots as equivalent for version numbers)
2. Update fallback chain model IDs to match what copilot actually serves
3. Add provider-specific model ID aliases

Additional Context

Discovered while trying to use github-copilot as the sole Claude provider (anthropic disconnected). All copilot Claude entries in the fallback chains are affected.

[mrm007]

Root cause found: Model IDs come from models.dev/api.json. The same model has different IDs per provider:

• anthropic → claude-opus-4-6 (hyphens)
• github-copilot → claude-opus-4.6 (dots)

$ curl -s "https://models.dev/api.json" | jq '."anthropic".models | keys[] | select(startswith("claude-opus-4"))'
"claude-opus-4-6"

$ curl -s "https://models.dev/api.json" | jq '."github-copilot".models | keys[] | select(startswith("claude-opus-4"))'
"claude-opus-4.6"

The fallback chains use the anthropic-style ID for all providers in the array, but models.dev defines them differently per provider. The fix likely needs per-provider model ID mapping in the fallback entries, or normalization during resolution.