MergeConfigPr approvals had a fully-implemented approve handler
(run_merge_config_pr, ff_push_to_main, mark_pr_merged) and dashboard
display, but no way to submit one. An agent with the `approvals` tool
group calling request_merge_config_pr(agent, pr_number) is the missing
piece.
What this adds:
- RequestMergeConfigPr variant in hive-sh4re AgentRequest + ToolGroup::Approvals
- submit_merge_config_pr: fetches PR head sha (the drift-gate reviewed sha),
queues a MergeConfigPr row, sets fetched_sha, emits approval_added with
pr_number so the dashboard card links to the forge PR
- handle_request_merge_config_pr: topology (require_descendant) +
tool-group (require_group(approvals)) guards before submit
- socket_server/mod.rs: dispatch arm for RequestMergeConfigPr
- hive-ag3nt MCP tool: request_merge_config_pr with full description
- docs/tools/lifecycle.md: documents the new tool + boundary table row
Unlike submit_apply_commit, no flake pre-flight at submission time (eval-
verify happens at approval time inside run_merge_config_pr, same as the
rest of the merge pipeline). Applied repo must already exist (guard added
with a clear error message pointing at request_apply_commit for first-spawn).
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