[backport] Issue dependency read/write tools (upstream main) #14

Summary

Two new feature-flagged tools for issue blocked-by/blocking relationships, gated behind the issue_dependencies feature flag (auto-enabled for insiders):

• issue_dependency_read: get_blocked_by / get_blocking via Issue.blockedBy / Issue.blocking GraphQL connections, cursor-paginated
• issue_dependency_write: add / remove × blocked_by / blocking via addBlockedBy / removeBlockedBy mutations; accepts issue numbers, resolves to node IDs in a single aliased query; self-dependency rejected before any round-trip

New file: pkg/github/issue_dependencies.go (448 lines) with AddBlockedByInput and RemoveBlockedByInput GraphQL input types, dependencyConnection structs, and tool registrations in tools.go + feature_flags.go.

Upstream reference

• version: upstream main (post v1.4.0, unreleased)
• commits: github@067756a
• PR: Add issue dependency read/write MCP tools github/github-mcp-server#2751

Fork conflict

Mild design consideration. The fork has issue_graph which traverses issue hierarchies (sub-issues, body references, timeline cross-references) via BFS. Blocked-by/blocking relationships are a separate relationship axis not yet covered by issue_graph. The upstream adds standalone tools; the fork might prefer these integrated into issue_graph's traversal. However, the standalone tools are additive and don't break issue_graph.

Context

Fills the MCP gap behind the gh CLI's gh issue block / gh issue unblock verbs (cli/cli#13057). Agents working with issue dependency graphs now have read and write access to the full relationship graph without needing the CLI.