Refactor collaborator permission fetch to use unified response-body guards

[Copilot]

FetchCollaboratorPermission duplicated nil-response / nil-body checks that are already implemented in httputil.ReadResponseBody, creating dead code and divergent error paths. This change removes the redundant caller-side guards and standardizes error handling through the shared helper.

• Response handling cleanup

  • Removed manual resp == nil and resp.Body == nil checks in internal/githubhttp/collaborator.go.
  • Delegated all response/body validation to httputil.ReadResponseBody.

• Error context normalization

  • Updated helper context from "GitHub API" to "GitHub collaborator API" so delegated errors remain operation-specific without custom guard logic.

• Test expectation alignment

  • Updated internal/githubhttp/collaborator_test.go assertions to match the new authoritative error messages emitted by ReadResponseBody.

• Related pattern audit

  • Reviewed internal/githubhttp/visibility.go for the same duplicate guard pattern; no equivalent pre-check duplication was found.

// before
if resp == nil {
    return nil, fmt.Errorf("failed to fetch response: nil response returned without error")
}
if resp.Body == nil {
    return nil, fmt.Errorf("failed to fetch response: response body is nil")
}
body, err := httputil.ReadResponseBody(resp, "GitHub API")

// after
body, err := httputil.ReadResponseBody(resp, "GitHub collaborator API")

[Copilot]

Pull request overview

This PR refactors FetchCollaboratorPermission to rely on the shared httputil.ReadResponseBody helper for response/body validation and HTTP error handling, eliminating redundant caller-side guards and standardizing error messages for GitHub collaborator permission fetches.

Changes:

• Removed redundant resp == nil / resp.Body == nil checks from FetchCollaboratorPermission, delegating to httputil.ReadResponseBody.
• Updated the helper context string to "GitHub collaborator API" so returned errors are operation-specific.
• Updated unit test assertions to match the new error message prefixes.

Show a summary per file

File	Description
internal/githubhttp/collaborator.go	Removes duplicate response/body guards and switches ReadResponseBody context to collaborator-specific wording.
internal/githubhttp/collaborator_test.go	Aligns error-message assertions with the new context-driven ReadResponseBody error strings.

Review details

Tip

Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Low