Judge a pull request into a release branch by that branch's controller and repositories

A release branch could never carry a change that needs another repository's
release-branch change: its pull requests were judged by the running controller
and against the other repositories' main (hq issue 704, ADR 0358).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

cmd/mesh-controller/checks.go

@@ -3,6 +3,7 @@ package main
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"path"
 	"regexp"
@@ -248,30 +249,14 @@ func checkRequestFor(ctx context.Context, open *stores, p link.PullUpdated, scop
 	if err != nil {
 		return link.BuildRequest{}, err
 	}
-	// Beside it, at what the mesh runs: each core repository by the module the mesh builds from it.
-	beside := map[string]link.CheckedOut{}
-	for _, e := range entries {
-		dir, core := coreModules[e.Manifest.Module]
-		if !core || e.Provided || e.Source.Repository == "" {
-			continue
-		}
-		url, err := clone(e.Source)
-		if err != nil {
-			return link.BuildRequest{}, err
-		}
-		refs := besideRefs(dir, current[e.Manifest.Module].Commit)
-		beside[dir] = link.CheckedOut{Repository: url, Ref: refs[dir]}
-		if dir == "mesh-controller" {
-			beside["mesh-controller-main"] = link.CheckedOut{Repository: url, Ref: refs["mesh-controller-main"]}
-			if e.Source.Seat != "" {
-				for _, sibling := range []string{"mesh-lab", "mesh-sdk"} {
-					if url, err := clone(inventory.Source{Seat: e.Source.Seat, Repository: siblingOf(e.Source.Repository,
-						sibling)}); err == nil {
-						beside[sibling] = link.CheckedOut{Repository: url, Ref: refs[sibling]}
-					}
-				}
-			}
-		}
+	// **A pull request into a release branch is judged by that branch** (novox/hq ADR 0358): asked of the forge once.
+	release, err := releaseBranchOf(ctx, p, scope, entries)
+	if err != nil {
+		return link.BuildRequest{}, err
+	}
+	beside, err := besideOf(entries, func(module string) string { return current[module].Commit }, clone, release)
+	if err != nil {
+		return link.BuildRequest{}, err
 	}
 	builds := checkBuildsOf(p, scope, entries, clone)
 	return link.BuildRequest{
@@ -283,10 +268,142 @@ func checkRequestFor(ctx context.Context, open *stores, p link.PullUpdated, scop
 		Source:     sourceOnSeat(source),
 		Check: &link.CheckRequest{Owner: p.Owner, Repo: p.Repo, Number: p.Number, Base: p.Base,
 			Paths: p.Paths, Beside: beside, Modules: scope.Modules, Dependents: scope.Dependents, New: scope.New,
-			Manifests: scope.Manifests, Judge: scope.Judge, Builds: builds, Named: namedForTheCheck(ctx, p, builds)},
+			Manifests: scope.Manifests, Judge: scope.Judge, Builds: builds, Named: namedForTheCheck(ctx, p, builds),
+			Release: release},
 	}, nil
 }
 
+// besideOf is what a check reads beside its own repository, by the directory it is found under: each core repository
+// by the module the mesh builds from it, at besideRefs — or, for a pull request into a release branch (novox/hq ADR
+// 0358 §3), at its branch of that name where it has one and at its trunk otherwise, the controller's main kept for
+// its judge. running is the commit the mesh runs of a module.
+func besideOf(entries []inventory.Entry, running func(module string) string,
+	clone func(inventory.Source) (string, error), release string) (map[string]link.CheckedOut, error) {
+	beside := map[string]link.CheckedOut{}
+	for _, e := range entries {
+		dir, core := coreModules[e.Manifest.Module]
+		if !core || e.Provided || e.Source.Repository == "" {
+			continue
+		}
+		url, err := clone(e.Source)
+		if err != nil {
+			return nil, err
+		}
+		refs := besideRefs(dir, running(e.Manifest.Module))
+		at := func(dir, trunk string) link.CheckedOut {
+			if release == "" {
+				return link.CheckedOut{Repository: url, Ref: refs[dir]}
+			}
+			if trunk == "" {
+				trunk = "main"
+			}
+			return link.CheckedOut{Repository: url, Ref: release, Else: trunk}
+		}
+		beside[dir] = at(dir, followedBranch(e.Source.Ref))
+		if dir == "mesh-controller" {
+			// The controller's main stays its main: it judges only a check the running controller predates.
+			beside["mesh-controller-main"] = link.CheckedOut{Repository: url, Ref: refs["mesh-controller-main"]}
+			if release != "" {
+				// mesh-controller has the release branch: that is what makes it one (ADR 0358 §1).
+				beside[dir] = link.CheckedOut{Repository: url, Ref: release}
+			}
+			if e.Source.Seat != "" {
+				for _, sibling := range []string{"mesh-lab", "mesh-sdk"} {
+					if url, err := clone(inventory.Source{Seat: e.Source.Seat, Repository: siblingOf(e.Source.Repository,
+						sibling)}); err == nil {
+						b := link.CheckedOut{Repository: url, Ref: refs[sibling]}
+						if release != "" {
+							b = link.CheckedOut{Repository: url, Ref: release, Else: "main"}
+						}
+						beside[sibling] = b
+					}
+				}
+			}
+		}
+	}
+	return beside, nil
+}
+
+// releaseBranchOf is the release branch a pull request merges into (novox/hq ADR 0358 §1): its base, when that is not
+// its repository's trunk and mesh-controller has a branch of that name; empty otherwise, and the pull request is
+// checked as before it. **A base that is a trunk asks nothing**: main, the branch a module built from the repository
+// follows, or mesh-controller's own trunk. Any other base is asked of the forge once, and an answer it cannot give is
+// an error, never read as "no release branch".
+func releaseBranchOf(ctx context.Context, p link.PullUpdated, scope checkScope, entries []inventory.Entry) (string, error) {
+	base := p.Base
+	if base == "" || base == "main" {
+		return "", nil
+	}
+	if scope.From != nil && base == followedBranch(scope.From.Source.Ref) {
+		return "", nil
+	}
+	var controller *inventory.Entry
+	for i, e := range entries {
+		if e.Manifest.Module == "mesh-controller" && !e.Provided && e.Source.Repository != "" {
+			controller = &entries[i]
+			break
+		}
+	}
+	if controller == nil || base == followedBranch(controller.Source.Ref) {
+		return "", nil
+	}
+	if !tryRef.MatchString(base) || strings.Contains(base, "..") {
+		return "", nil // no branch the forge could hold: checked as before
+	}
+	owner, repo := sourceOwner(controller.Source.Repository), sourceName(controller.Source.Repository)
+	if owner == "" || repo == "" {
+		return "", nil
+	}
+	has, err := forgeHasBranch(ctx, owner, repo, base)
+	if err != nil {
+		return "", fmt.Errorf("whether %s/%s#%d merges into a release branch cannot be told — the forge did not say "+
+			"whether %s/%s has a branch %s (novox/hq ADR 0358): %w", p.Owner, p.Repo, p.Number, owner, repo, base, err)
+	}
+	if !has {
+		return "", nil
+	}
+	return base, nil
+}
+
+// sourceName is the name of a recorded repository, a path on the git seat or a URL: novox/mesh-host → mesh-host.
+func sourceName(repository string) string {
+	parts := strings.Split(strings.Trim(strings.TrimSuffix(repository, ".git"), "/"), "/")
+	if len(parts) < 2 {
+		return ""
+	}
+	return parts[len(parts)-1]
+}
+
+// forgeHasBranch asks the forge, through its module's tools on the bus, whether a repository has a branch. A
+// variable so a test needs no forge.
+var forgeHasBranch = func(ctx context.Context, owner, repo, branch string) (bool, error) {
+	js, err := aBus()
+	if err != nil {
+		return false, err
+	}
+	defer js.Close()
+	raw, _ := json.Marshal(map[string]any{"path": "/repos/" + owner + "/" + repo + "/branches/" + branch})
+	answer, err := link.Ask(ctx, link.OverNATS{Conn: js.Conn()}, "gitea", "gitea_api", raw, 30*time.Second)
+	if err != nil {
+		return false, err
+	}
+	if answer.Error != "" {
+		if strings.Contains(answer.Error, " 404 ") {
+			return false, nil
+		}
+		return false, errors.New(answer.Error)
+	}
+	var found struct {
+		Result struct {
+			Name string `json:"name"`
+		} `json:"result"`
+	}
+	if err := json.Unmarshal(answer.Result, &found); err != nil {
+		return false, err
+	}
+	return found.Result.Name == branch, nil
+}
+
 // namedForTheCheck are the builds earlier checks of the same pull request at the same head named, read once for the
 // check (novox/hq issue 703): asked again because only the trunk moved, the check keeps what they built of a key
 // still the same. Another pull request's build, or one of an earlier head, is never kept. None when they cannot be
@@ -458,6 +575,7 @@ func checkedOf(result link.BuildResult) link.Checked {
 		// repositories read beside it.
 		c.Trunk, c.Beside, c.Took = result.Check.Trunk, result.Check.Beside, result.Check.Took
 		c.Built = result.Check.Built
+		c.Release, c.JudgedBy, c.BesideAt = result.Check.Release, result.Check.JudgedBy, result.Check.BesideAt
 		if c.Gate == nil {
 			// A build seat from before the layers: its verdict is the gate's.
 			c.Gate = &link.CheckLayer{Verdict: c.Verdict, Summary: c.Summary}