👔 Enhance hostname normalization

[stoe]

This PR enhances GitHub API hostname handling to properly support GitHub Enterprise Cloud with Data Residency (GHEC+DR) regional domains while preserving existing behavior for GitHub Enterprise Server (GHES) instances. It also adds a helper to improve test reliability and strengthens hostname-related test coverage.

🔍 Changes

• Updated src/github/octokit.js hostname normalization:
  • region.ghe.com → https://api.region.ghe.com
  • api.region.ghe.com stays https://api.region.ghe.com (no /api/v3 appended)
  • Any other custom host (e.g. ghe.internal.example.com) → https://<host>/api/v3
  • No hostname → https://api.github.com
• Added named export getBaseUrl(octokit) to safely introspect the resolved API base URL.
• Strengthened test/github/octokit.test.js by:
  • Resetting module state per test via dynamic imports.
  • Asserting actual baseUrl values instead of placeholder checks.
  • Adding explicit tests for default, GHES, GHEC+DR, and already api.-prefixed regional hosts.
• Ensured overall suite remains green (216 tests passing) with slight coverage improvement for branch logic.

🤔 Rationale

Previously, any provided hostname was coerced into the GHES pattern with /api/v3. GHEC+DR regional endpoints (*.ghe.com) instead use an api. subdomain (e.g. api.region1.ghe.com) without /api/v3. The old logic produced incorrect URLs for these environments, breaking API calls. This update corrects that and avoids double-prefixing when the user already supplies an api. host.

🛠 Implementation Details

Logic branch in octokit.js:

• Detect *.ghe.com via regex.
• If not already api.-prefixed, add api..
• Preserve already api.-prefixed domains.
• Apply /api/v3 only to non-public, non-*.ghe.com custom hosts.
• Fallback to https://api.github.com when no hostname is provided.
• Exported getBaseUrl() helper (additive, non-breaking) for introspection/testing.

✅ Testing

Updated octokit.test.js:

• Dynamic import after jest.resetModules() to isolate singleton state.
• Assertions on client.request.endpoint.DEFAULTS.baseUrl for all hostname variants.
• Added test for preserving already api.-prefixed regional hosts.

Result: 216 tests passing, coverage ~87% statements / ~88% branches.

🔄 Backward Compatibility

• Public API for getOctokit unchanged.
• Existing GHES behavior intact.
• Only difference: *.ghe.com now resolves correctly; already api. prefixed hosts no longer risk unintended /api/v3 suffixes.
• Added export is purely additive.

📈 Impact / Risk

Low risk: Narrow conditional change, fully covered by targeted tests.

📝 Checklist

• Code changes implemented
• Tests updated / added
• All tests passing locally
• No breaking changes
• README hostname section (pending / optional)

[Copilot]

Pull Request Overview

This PR enhances GitHub API hostname handling to properly support GitHub Enterprise Cloud with Data Residency (GHEC+DR) regional domains while preserving existing behavior for GitHub Enterprise Server (GHES) instances.

• Adds logic to detect *.ghe.com domains and prefix them with api. instead of appending /api/v3
• Introduces a getBaseUrl() helper function for introspecting resolved API base URLs
• Replaces placeholder tests with concrete assertions using dynamic imports to isolate module state

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/github/octokit.js	Enhanced hostname normalization logic and added getBaseUrl helper
test/github/octokit.test.js	Replaced placeholder tests with concrete hostname normalization tests
readme.md	Added comprehensive hostname handling documentation table

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