feat: Add REST API method support for assign_to_agent

[Copilot]

Adds REST API support for Copilot agent assignment per the December 2025 GitHub API update, alongside existing GraphQL support.

Changes

• New api-method option in assign-to-agent config: graphql (default) or rest
• REST API implementation using POST /repos/{owner}/{repo}/issues/{issue_number}/assignees with agent_assignment object
• Environment variable GH_AW_AGENT_API_METHOD passed to job for runtime routing
• Staged preview and step summary now display the API method used

Usage

safe-outputs:
  assign-to-agent:
    api-method: rest  # or "graphql" (default)
    # All existing options work with both methods:
    # target_repository, base_branch, custom_instructions, custom_agent

REST API Format

Per GitHub community discussion:

{
  "assignees": ["copilot-swe-agent[bot]"],
  "agent_assignment": {
    "target_repo": "owner/repo",
    "base_branch": "main",
    "custom_instructions": "...",
    "custom_agent": "..."
  }
}

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[Copilot]

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• github.blog
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node /home/REDACTED/work/_temp/ghcca-node/node/bin/node --enable-source-maps /home/REDACTED/work/_temp/copilot-developer-action-main/dist/index.js (dns block)
• https://api.github.com/user
  • Triggering command: /usr/bin/gh gh api user --jq .login 5 GO111MODULE ache/go/1.25.0/x64/bin/go GOINSECURE parser GOMODCACHE go env ITAbVvSQ4 GO111MODULE (http block)
  • Triggering command: /usr/bin/gh gh api user --jq .login -json GO111MODULE /opt/hostedtoolcache/go/1.25.0/x64/bin/go GOINSECURE GOMOD GOMODCACHE go env tformat GO111MODULE e71869f3 GOINSECURE GOMOD GOMODCACHE 1658961/b332/fil/home/REDACTED/work/gh-aw/gh-aw/gh-aw (http block)
  • Triggering command: /usr/bin/gh gh api user --jq .login -json GO111MODULE 7355dfb3cd4b54dabdae6c042e479e881d5/log.json GOINSECURE GOMOD GOMODCACHE ps -go.�� -go.git GO111MODULE e/git-remote-https GOINSECURE GOMOD GOMODCACHE e/git-remote-htt-address (http block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)