Add parentIssue support to GitHubClient.createIssue for sub-issue functionality

[Copilot]

This PR implements support for creating GitHub sub-issues by adding an optional parentIssue parameter to the GitHubClient.createIssue() method. When provided, the created issue is automatically linked as a sub-issue to the specified parent issue.

Problem

The GitHub client's createIssue method did not support creating sub-issues (child issues linked to a parent issue), which is a common workflow pattern for breaking down large features or epics into smaller, manageable tasks.

Solution

Enhanced the createIssue method to accept a parentIssue option that:

1. Creates the issue normally using GitHub's REST API
2. Establishes parent-child relationship via GraphQL createTaskListItem mutation
3. Handles errors gracefully - issue creation succeeds even if sub-issue linking fails

Usage

// Create a parent epic
const epic = await github.createIssue("Epic: User Authentication", "...");

// Create linked sub-issues
const subIssue = await github.createIssue("Sub-task: Login Form", "...", {
  parentIssue: epic.number,
  labels: ["frontend", "sub-task"]
});

Changes Made

• Type Definition: Added parentIssue?: number | string to GitHubIssueCreateOptions
• Implementation: Modified createIssue to extract parentIssue and call new addSubIssue method
• GraphQL Integration: Added private addSubIssue method using GitHub's task list API
• Documentation: Updated GitHub reference docs with examples and API summary
• Testing: Added comprehensive tests covering both scenarios (with/without parentIssue)
• Sample Script: Added github-sub-issues.genai.mts demonstrating practical usage

Implementation Details

The implementation is minimal and non-breaking:

• Existing code continues to work unchanged
• parentIssue is extracted before REST API call to avoid parameter conflicts
• Uses proper GraphQL mutation with node IDs for reliable linking
• Includes debug logging and error handling
• Graceful degradation ensures main operation always succeeds

Sample Script

The included GenAIScript sample (samples/sample/genaisrc/github-sub-issues.genai.mts) demonstrates:

• Creating a parent epic issue with proper labeling
• Automatically generating multiple sub-issues for different project phases
• Using the parentIssue parameter to establish relationships
• Real-world project management workflow patterns
• Error handling and user feedback

This provides developers with a complete example of how to leverage sub-issues for organizing complex projects and breaking down large features into manageable tasks.

Testing

• ✅ New functionality tested with mocked GraphQL calls
• ✅ Backward compatibility verified (existing usage unchanged)
• ✅ Build passes without compilation errors
• ✅ All existing tests continue to pass
• ✅ Sample script demonstrates practical usage

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[pelikhan]

@copilot add a GenAIScript sample script under samples/sample that uses this feature.

[Copilot]

@copilot add a GenAIScript sample script under samples/sample that uses this feature.

Added GenAIScript sample github-sub-issues.genai.mts in samples/sample/genaisrc/ that demonstrates the parentIssue feature. The script creates a parent epic and automatically generates linked sub-issues showing practical project management workflow. Commit: afaa73c