feat: auto-assign relevant reviewers based on past contributions

[ymelois]

---

Note

This PR adds automatic reviewer assignment by parsing CODEOWNERS rules and scoring candidates based on file ownership and past commit history. It introduces a ReviewerService domain, new GitHub client methods (fetch_codeowners, fetch_pr_files, fetch_file_contributors, request_reviewers), and comprehensive unit tests.

^{Written by Mendral for commit e6abba3.}

[pratrol]

Pratrol Triage Brief: 🟢 High Confidence

Pratrol assessed this pull request across the primary risk vectors below.

Risk Vector	Score	Tier
Contributor Context	72/100	🟢 High
Logic Risk (Mistral)	83/100	🟢 High
Overall Confidence	79/100	🟢 High

Summary: Added functionality to auto-assign reviewers based on CODEOWNERS and past contributions.

Key Signal: The PR introduces a new domain for reviewer assignment with comprehensive tests.

Recommendation: Review the new reviewer assignment logic and test cases thoroughly.

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[mendral-app]

🤖 Code Review

Assessment ⚠️

The pagination bug from the previous review was fixed — fetch_pr_files now correctly paginates up to 3000 files. The partition_owners org-validation concern remains unaddressed. No new high-severity issues found in the new code.

Note

Tag @mendral-app with feedback or questions. View session

[mendral-app]

🐛 bug (medium)

Previous comment not addressed: partition_owners strips the org prefix from team slugs without validating that the org matches the repo owner. If a CODEOWNERS file references a team from a different org (e.g. other-org/team), the slug is passed to the GitHub API which will silently fail or assign the wrong team. The org prefix should be validated against owner before accepting the team.

📝 Suggested change

Suggested change

	pub fn partition_owners(owners: &HashSet<String>) -> (Vec<String>, Vec<String>) {
	let mut users = Vec::new();
	let mut teams = Vec::new();
	for owner in owners {
	if let Some((_org, team)) = owner.split_once('/') {
	teams.push(team.to_owned());
	} else {
	users.push(owner.clone());
	}
	}
	(users, teams)
	}
	pub fn partition_owners(owners: &HashSet<String>, repo_owner: &str) -> (Vec<String>, Vec<String>) {
	let mut users = Vec::new();
	let mut teams = Vec::new();
	for owner in owners {
	if let Some((org, team)) = owner.split_once('/') {
	if org != repo_owner {
	warn!(
	message = "CODEOWNERS team org does not match repo owner, skipping.",
	team = %owner,
	);
	continue;
	}
	teams.push(team.to_owned());
	} else {
	users.push(owner.clone());
	}
	}
	(users, teams)
	}