summary.yml: migrate off actions/ai-inference v2 (github-models removed upstream in v3)

[d-morrison]

Split out of #834, which is the hotfix (pin back to v2, ignore majors). This is the migration that pin defers.

Why v2 is a dead end, not a resting place

actions/ai-inference v3 did not merely change an interface. Upstream removed the github-models transport outright -- release notes name PR #236, "remove github-models support and make copilot the only provider", and the v3 README states "The action is Copilot-only". So v2 is the last major carrying the endpoint summary.yml uses, and it will receive no further work on that path.

This compounds with #617: summary.yml's own header already notes that GitHub Models is in scheduled retirement brownout, and #617's title is "summary.yml targets the retiring GitHub Models endpoint and 410s on every run". The transport is being retired from both ends at once.

What migrating actually requires

Not a pin bump:

• install and authenticate the GitHub Copilot CLI on the runner before the action runs (it is not pre-installed on GitHub-hosted runners, per the v3 README);
• drop the endpoint input, which no longer exists;
• change model from openai/gpt-4o-mini to a value the Copilot CLI accepts (e.g. gpt-4.1, claude-sonnet-4.5);
• re-check the token semantics, and whether secrets.API_KEY/OPENAI_API_KEY still mean anything on the Copilot path.

Then update COMPATIBLE_ACTION in .github/workflows/scripts/tests/run-summary-workflow-tests.py and the ignore entry #834 adds to .github/dependabot.yml.

Alternatives worth weighing first

Given #617, retiring or re-implementing summary.yml may beat migrating it. Decide that before doing the Copilot-CLI work.

Posted by Claude Code (AI agent) --- not written by a human.