[backport] Promote issue fields to default, remove legacy issue_write methods (upstream main)

[gastrodon]

Summary

Removes the remote_mcp_issue_fields feature flag and promotes issue field support to always-on. Simultaneously deletes the legacy issue_write write methods that pre-dated issue field support (~572 lines removed from issues.go). The granular issue_write tool (with issue_fields param) is now the only write path.

Files changed: pkg/github/issues.go -572 lines; pkg/github/feature_flags.go -7 lines; pkg/github/issue_fields.go -2; pkg/github/tools.go -2; pkg/github/ui_tools.go -4; removed __toolsnaps__/issue_write_ff_remote_mcp_issue_fields.snap and list_issues_ff_remote_mcp_issue_fields.snap.

Upstream reference

• version: upstream main (post v1.4.0, unreleased)
• commits: github@a378370
• PR: Promote issue fields and deprecate legacy issue write tool  github/github-mcp-server#2696

Fork conflict

None. The fork does not extend the legacy issue_write methods or the remote_mcp_issue_fields flag. The fork's issue_graph, set_project_item_status, and add_issue_to_project tools are independent.

Context

The remote_mcp_issue_fields flag was a graduation mechanism for the new granular issue_write tool. Having confirmed stability, upstream removed the flag and the legacy code it guarded. This reduces maintenance surface and eliminates two parallel code paths.

[gastrodon]

Unified Changelog — upstream main since v1.4.0

See #10 for the full changelog. Summary:

• [backport] OAuth 2.1 stdio login (upstream main) [story] #13 (story): OAuth 2.1 stdio login → sub-issues [backport] OAuth 2.1 core library — PKCE + device flows (upstream main) #10 [backport] Wire OAuth 2.1 login into stdio server (upstream main) #11 [backport] OAuth build-time credentials + docs (upstream main) #12
• [backport] Issue dependency read/write tools (upstream main) #14: Issue dependency read/write tools
• [backport] get_parent method for issue_read (upstream main) #15: get_parent for issue_read
• [backport] Promote issue fields to default, remove legacy issue_write methods (upstream main) #16: Promote issue fields, remove legacy issue_write
• [backport] Remove show_ui parameter, centralize show/defer decision (upstream main) #17: Remove show_ui, centralize show/defer
• [backport] Fix delete:true on issue fields — REST DELETE fallback (upstream main) #18: Fix delete:true on issue fields
• [backport] Bound ui_get pagination to prevent latency spikes (upstream main) #19: Bound ui_get pagination
• [backport] Fix issue_write MCP App form gating for labels/assignees/milestone/type (upstream main) #20: Fix issue_write form gating
• [backport] Validate required params in add_comment_to_pending_review (upstream main) #21: Validate required params in add_comment_to_pending_review

[gastrodon]

No-op. The fork has no remote_mcp_issue_fields feature flag in feature_flags.go, no legacy issue_write methods in issues.go (confirmed: 0 occurrences), and the __toolsnaps__/issue_write_ff_remote_mcp_issue_fields.snap and list_issues_ff_remote_mcp_issue_fields.snap files are absent. Promotion is already in effect.