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Archon PR Review

Archon is an architecture analysis tool that extracts package-level dependency graphs from Go repositories and diffs them between commits. The /archon-pr-review CI command runs Archon on a pull request and reports whether the PR changes the architecture or is purely internal.

How to Use

Comment on any PR:

/archon-pr-review

The GitHub Action runs automatically and posts a comment with the results.

What It Reports

Empty Delta (No Architectural Change)

If the PR only changes internal implementation (file renames, function body rewrites, new files within existing packages without new exports), Archon reports:

No architectural change detected. Internal-only PR — fast-track eligible.

If tests (invariants) were added, removed, or modified, those are listed separately — even when the structure is unchanged.

Non-Empty Delta (Architecture Changed)

If the PR changes package boundaries, Archon reports three sections:

1. Architectural Delta — What structurally changed:

  • + arrow A -> B [import] — new dependency between packages
  • - arrow A -> B [import] — removed dependency
  • + surface pkg.Func — package surface widened (new export)
  • - surface pkg.Func — package surface narrowed (export removed)
  • + box pkg / - box pkg — new or removed package

2. Blast Radius — For each changed package, how many other packages depend on it (directly and transitively). High blast radius means a change there affects many things.

3. Contract Evidence — For each interface (contract) in the codebase, which implementations are covered by a contract test and which are not. Gaps are flagged.

How It Works

  1. Determines the merge-base and PR head SHA
  2. Runs archon-go delta --json to detect structural changes
  3. If empty: posts fast-track message
  4. If non-empty: runs archon-go delta (human report), archon-go impact (blast radius per changed package), and archon-go evidence (contract test coverage)
  5. Posts combined output as a PR comment

Key Properties

  • Witness-only changes are invisible. A file rename or function body edit within a package does not appear in the delta. Only boundary-crossing changes (new dependencies, new/removed exports, new/removed packages) are reported.
  • Deterministic. Same commits always produce the same output.
  • No LLM involved. Pure static analysis. For LLM-interpreted results, see /archon-pr-review-claude (#1540).

Requirements

  • The repository must be a Go module
  • The commenter must have write access to the repository
  • Archon is built from archon v0.1.0 during the CI run
  • Issue: #1541
  • Future: #1540 — /archon-pr-review-claude feeds Archon output to Claude for a reasoned architectural review