Implement label attachment in discussion-manager agent

[anettodev]

Summary

The discussion-builder/SKILL.md now defines label attachment rules for GitHub Discussions, but the discussion-manager agent (src/agents/discussion-manager.md) does not implement them. Labels are never attached when /plan-discussion creates a discussion.

Expected Behavior

After creating a discussion, the agent should:

1. Run gh label list to fetch existing repo labels
2. Match labels based on the discussion type (per the mapping table in SKILL.md)
3. Auto-attach matching labels that already exist
4. For missing suggested labels, propose name + color and wait for user approval before creating
5. Use the GraphQL addLabelsToLabelable mutation to attach labels (REST endpoints do not support discussion labels)

Label Mapping to Implement

Type	Auto-attach if exists	Suggest creating if not
design	enhancement, architecture	design (#0075ca)
decision	architecture	decision (#e4e669)
retro	—	retro (#f9d0c4)
postmortem	—	postmortem (#b60205)
distribution	—	distribution (#0e8a16)
analysis	—	analysis (#5319e7)

Files to Update

• src/agents/discussion-manager.md — add label resolution and attachment steps after discussion creation

Notes

• Labels on discussions require GraphQL (addLabelsToLabelable) — the REST /labels endpoint only works for issues
• The discussion node ID is returned by the createDiscussion mutation and must be passed to addLabelsToLabelable
• Label node IDs must be fetched via GraphQL before attaching

Relates to discussion #1.

[anettodev]

Implemented in src/agents/discussion-manager.md:

• Added step 6 (Resolve and Attach Labels) with three sub-steps:
  • 6a: Fetch all repo labels (name + node ID) via GraphQL
  • 6b: Apply the type→label mapping — auto-attach existing labels silently, propose creation for missing suggested labels and wait for user approval
  • 6c: Attach collected label node IDs to the discussion via addLabelsToLabelable GraphQL mutation
• Step 5 now queries the discussion node ID after creation (required for GraphQL label attachment)
• Removed the incorrect REST endpoint (/discussions/N/labels) that was silently failing
• Report output now includes the attached labels