fix: Use simple GraphQL mutation for backward compatibility when no Copilot options provided

[Copilot]

The assign_to_agent safe output was failing because the GraphQL mutation always declared $copilotAssignmentOptions: CopilotAssignmentOptionsInput even when no options were provided. This type isn't yet available in all API contexts, breaking existing workflows.

Changes

• Conditional mutation selection: Use simple mutation (no copilotAssignmentOptions) for basic assignment, extended mutation only when new options are actually provided
• Updated tests: Added test for simple mutation path, existing tests now verify headers only appear with Copilot options

Behavior

# Basic usage - uses simple mutation (backward compatible)
- assign_to_agent:
    issue_number: 123

# With options - uses extended mutation with GraphQL-Features header
- assign_to_agent:
    issue_number: 123
    base_branch: "develop"
    custom_instructions: "Follow coding standards"

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✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[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:

• https://api.github.com/user
  • Triggering command: /usr/bin/gh gh api user --jq .login ut.js GO111MODULE .cfg GOINSECURE GOMOD GOMODCACHE ache/go/1.25.0/x64/pkg/tool/linu--auto env 1737-12059/test-258474244 GO111MODULE 1737-12059/test-258474244/.gitattributes GOINSECURE GOMOD GOMODCACHE ache/go/1.25.0/x64/pkg/tool/linu--jq (http block)
  • Triggering command: /usr/bin/gh gh api user --jq .login -json GO111MODULE ache/go/1.25.0/x64/pkg/tool/linux_amd64/vet GOINSECURE GOMOD GOMODCACHE ache/go/1.25.0/x64/pkg/tool/linu/var/run/docker/runtime-runc/moby (http block)
  • Triggering command: /usr/bin/gh gh api user --jq .login -json GO111MODULE 88c7bd9b816830ab12b4a34cba560fd58fc/log.json GOINSECURE GOMOD GOMODCACHE go env ns/setup.git GO111MODULE (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)