fix: align GitHub Copilot model variants with catalog

[divlook]

Summary

• align GitHub Copilot fallback variants with the current opencode models github-copilot --verbose output by splitting Copilot-specific Opus and Gemini entries from shared fallback chains
• add regression coverage for requirements, compatibility, runtime capability normalization, model-fallback flows, and plugin-entry isolation
• verify the change with bun run typecheck, bun test, and bun run build

Changes

• set GitHub Copilot claude-opus-4.6 fallback entries to variant: high because the current opencode models github-copilot --verbose output exposes only low, medium, and high
• remove explicit variant from GitHub Copilot gemini-3.1-pro-preview fallback entries because the current opencode models github-copilot --verbose output does not expose a Gemini variant set there
• update snapshot and regression expectations for the new fallback ordering
• isolate the auto-update plugin-entry test from local user config leakage

Testing

• bun run typecheck
• bun test
• bun run build

Notes

• target branch: dev
• communication for review should stay in English
• please ensure CLA requirements are satisfied before review/merge

[github-actions]

All contributors have signed the CLA. Thank you! ✅
_{Posted by the CLA Assistant Lite bot.}

[cubic-dev-ai]

No issues found across 8 files

Confidence score: 5/5

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

_{Auto-approved: Aligns GitHub Copilot variants with catalog capabilities, splitting fallback chains to ensure valid variant requests (e.g., high instead of max for Opus), backed by updated regression tests.}

[Copilot]

Pull request overview

Aligns GitHub Copilot-specific model fallback entries with the models.jsonl catalog by separating Copilot variants from shared fallback chains, and updates regression coverage to lock in the new ordering/normalization behavior.

Changes:

• Split shared fallback-chain entries into provider-specific siblings for Copilot Claude Opus (forcing variant: "high") and Copilot Gemini (omitting variant).
• Add/adjust tests covering settings compatibility and Copilot runtime capability normalization edge-cases.
• Update model-fallback tests/snapshots and isolate the auto-update plugin-entry test from user config leakage via an isolated config dir.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/shared/model-settings-compatibility.test.ts	Adds regression tests for Copilot variant handling when metadata limits variants / when variant is omitted.
src/shared/model-requirements.ts	Splits Copilot Claude Opus + Gemini entries from shared chains to match catalog expectations.
src/shared/model-requirements.test.ts	Updates ordering/length assertions to reflect split fallback entries.
src/shared/model-capabilities.test.ts	Adds tests for Copilot runtime metadata edge cases (object-form variants, empty variants object).
src/plugin/event.model-fallback.test.ts	Updates model-fallback expectations to prefer the new adjacent Copilot Opus split entry.
src/hooks/model-fallback/hook.test.ts	Updates fallback progression assertions to match the new chain ordering and Copilot Opus high variant.
src/hooks/auto-update-checker/checker/plugin-entry.test.ts	Prevents local user config contamination by forcing an isolated OPENCODE_CONFIG_DIR in the spawned process.
src/cli/snapshots/model-fallback.test.ts.snap	Snapshot updates reflecting new fallback ordering and Copilot variant behavior.

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[divlook]

I have read the CLA Document and I hereby sign the CLA

[divlook]

recheck

[divlook]

Follow-up cleanup for stale GitHub Copilot nano references is tracked separately in #3359. This PR intentionally keeps that work out of scope and only covers the Copilot variant alignment changes.