Use GraphQL UpdatePullRequestBranch mutation for conflict-free branch updates

[Copilot]

When updating a PR branch with no conflicts, use GitHub's native updatePullRequestBranch GraphQL mutation instead of manually orchestrating tree/commit creation via REST.

Changes

• GraphQL schema (queries.gql, queriesExtra.gql): Added UpdatePullRequestBranch mutation
• Types (graphql.ts): Added UpdatePullRequestBranchResponse interface
• Branch update logic (pullRequestModel.ts):
  • Route Mergeable/Behind states through new updateBranchWithGraphQL()
  • Preserve REST approach for Conflict state (requires manual resolution)
  • Unknown/NotMergeable states fall back to REST as defensive behavior

Before/After

Before: 5 REST calls (getBranch → getCommit → createTree → createCommit → updateRef)

After: 1 GraphQL mutation for clean updates

await mutate<UpdatePullRequestBranchResponse>({
  mutation: schema.UpdatePullRequestBranch,
  variables: {
    input: {
      pullRequestId: this.graphNodeId,
      expectedHeadOid: this.head.sha
    }
  }
});

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:

• update.code.visualstudio.com
  • Triggering command: /opt/hostedtoolcache/node/20.20.0/x64/bin/node node ./out/src/test/runTests.js (dns 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)

Original prompt

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This section details on the original issue you should resolve

<issue_title>Use the GH GraphQL API UpdatePullRequestBranch for pulling in updates when there are no conflicts</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Use the GH GraphQL API UpdatePullRequestBranch for pulling in updates when there are no conflicts #8231

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