Bring F3 up to its release branch, with both sides' store tests (part 4 of 14)

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

cmd/mesh-controller/template_test.go

@@ -0,0 +1,204 @@
+package main
+
+import (
+	"bytes"
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/novox/mesh-controller/internal/catalogue"
+	snapshot "github.com/novox/mesh-controller/internal/facts"
+	"github.com/novox/mesh-controller/internal/inventory"
+)
+
+// A file's text kept as a template file in its module's repository (novox/hq ADR 0349 §2, design 57 package T1,
+// issue 654): `module check` and the merge gate read it from the tree beside the manifest, so a change to a
+// template alone is judged as a change to its module.
+
+const templatedNotifier = `{"module":"notifier","version":"1",
+  "build":{"artifacts":[{"name":"files","kind":"archive","from":"files"}]},
+  "resources":[{"id":"conf","type":"file","path":"/etc/notifier/notifier.conf","mode":"0644","template":"files/notifier.conf"}]}`
+
+// inlineNotifier is the same module as the mesh holds it: built, its text inline.
+const inlineNotifier = `{"module":"notifier","version":"1",
+  "resources":[{"id":"conf","type":"file","path":"/etc/notifier/notifier.conf","mode":"0644","content":"volume = 3\n"}]}`
+
+// aTemplatedModule writes a module's directory: its manifest and its files/.
+func aTemplatedModule(t *testing.T, dir, manifest string, files map[string]string) string {
+	t.Helper()
+	if err := os.MkdirAll(dir, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	path := filepath.Join(dir, "module.json")
+	if err := os.WriteFile(path, []byte(manifest), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	for name, text := range files {
+		full := filepath.Join(dir, filepath.FromSlash(name))
+		if err := os.MkdirAll(filepath.Dir(full), 0o755); err != nil {
+			t.Fatal(err)
+		}
+		if err := os.WriteFile(full, []byte(text), 0o644); err != nil {
+			t.Fatal(err)
+		}
+	}
+	return path
+}
+
+func TestModuleCheckReadsTemplatesFromTheTreeBesideTheManifest(t *testing.T) {
+	good := aTemplatedModule(t, t.TempDir(), templatedNotifier, map[string]string{"files/notifier.conf": "volume = 3\n"})
+	var out bytes.Buffer
+	if err := moduleCheck([]string{good}, &out); err != nil || !strings.Contains(out.String(), "notifier: ok") {
+		t.Fatalf("a module with its text in files/ was refused: %v\n%s", err, out.String())
+	}
+
+	// A change to the template alone, to text the controller refuses inline, is refused the same.
+	bad := aTemplatedModule(t, t.TempDir(), templatedNotifier,
+		map[string]string{"files/notifier.conf": "volume = 3\nstore = ${dir:nowhere}\n"})
+	out.Reset()
+	if err := moduleCheck([]string{bad}, &out); err == nil || !strings.Contains(out.String(), "nowhere") {
+		t.Fatalf("a template whose text is refused inline passed:\n%s", out.String())
+	}
+
+	// A symlink under files/ that no template names: the build's packing refuses it, so the check does too.
+	linked := t.TempDir()
+	aTemplatedModule(t, linked, templatedNotifier, map[string]string{"files/notifier.conf": "volume = 3\n"})
+	if err := os.Symlink("/etc/hostname", filepath.Join(linked, "files", "elsewhere")); err != nil {
+		t.Fatal(err)
+	}
+	out.Reset()
+	if err := moduleCheck([]string{filepath.Join(linked, "module.json")}, &out); err == nil ||
+		!strings.Contains(out.String(), "files/elsewhere is a symlink") {
+		t.Fatalf("a symlink under files/ passed the check:\n%s", out.String())
+	}
+
+	// And a template the tree lacks, by name.
+	missing := aTemplatedModule(t, t.TempDir(), templatedNotifier, nil)
+	out.Reset()
+	if err := moduleCheck([]string{missing}, &out); err == nil || !strings.Contains(out.String(), "files/notifier.conf") {
+		t.Fatalf("a missing template was not refused by name:\n%s", out.String())
+	}
+}
+
+// templatedMesh is catalogueMesh with the notifier on the laptop, registered as built: its text inline.
+func templatedMesh(t *testing.T) (snapshot.Facts, map[string]string) {
+	t.Helper()
+	open := aMesh(t)
+	ctx := t.Context()
+	manifests := map[string]string{
+		"lemurs": `{"module":"lemurs","version":"1","capabilities":["systemd"],
+			"resources":[{"id":"service","type":"service","unit":"lemurs.service","state":"running","boot":"enabled"}]}`,
+		"notifier": inlineNotifier,
+	}
+	for name, raw := range manifests {
+		m, err := catalogue.ParseManifest([]byte(raw))
+		if err != nil {
+			t.Fatalf("%s: %v", name, err)
+		}
+		if err := open.inventory.RegisterModule(ctx, m, inventory.Source{Repository: "novox/mesh-catalog",
+			Path: "modules/" + name, BuiltFrom: "c0ffee"}); err != nil {
+			t.Fatal(err)
+		}
+		if _, err := assign(ctx, open, "laptop", name); err != nil {
+			t.Fatalf("assign %s: %v", name, err)
+		}
+	}
+	f, err := gatherFacts(ctx, open, "2.11.17")
+	if err != nil {
+		t.Fatal(err)
+	}
+	return f, manifests
+}
+
+// aTemplatedTree is the catalogue's checkout with the notifier's text in files/.
+func aTemplatedTree(t *testing.T, manifests map[string]string, text string, has bool) string {
+	t.Helper()
+	tree := aTree(t, withEdit(manifests, "notifier", ""))
+	files := map[string]string{}
+	if has {
+		files["files/notifier.conf"] = text
+	}
+	aTemplatedModule(t, filepath.Join(tree, "modules", "notifier"), templatedNotifier, files)
+	return tree
+}
+
+const notifierTemplate = "modules/notifier/files/notifier.conf"
+
+func TestTheMergeGateJudgesAChangeToATemplateAlone(t *testing.T) {
+	f, manifests := templatedMesh(t)
+
+	// The module moved to its template, the same text: nothing changes on any machine.
+	v := gateJudged(t, f, aTemplatedTree(t, manifests, "volume = 3\n", true), "modules/notifier/module.json",
+		notifierTemplate)
+	if v.Verdict == "fail" || v.Modules["notifier"] != "" {
+		t.Fatalf("the module moved to its template with the same text reads as a change (%v):\n%s", v.Modules, v.Report())
+	}
+
+	// The template alone changed: its module changed, and composes.
+	v = gateJudged(t, f, aTemplatedTree(t, manifests, "volume = 4\n", true), notifierTemplate)
+	if v.Verdict == "fail" || v.Modules["notifier"] != "changed" {
+		t.Fatalf("a change to the template alone is not a change to its module (%v):\n%s", v.Modules, v.Report())
+	}
+	if v.Width == nil || strings.Join(v.Width.Modules, ",") != "notifier" {
+		t.Fatalf("a change to the template rebuilds %+v, not its module", v.Width)
+	}
+
+	// The template alone changed to text the controller refuses: the pull request fails, naming the module.
+	v = gateJudged(t, f, aTemplatedTree(t, manifests, "store = ${dir:nowhere}\n", true), notifierTemplate)
+	if v.Verdict != "fail" || !strings.Contains(v.Report(), "notifier") {
+		t.Fatalf("a template the controller refuses passed the gate:\n%s", v.Report())
+	}
+
+	// A symlinked files/ fails: nothing is read from outside the tree.
+	tree := aTree(t, withEdit(manifests, "notifier", ""))
+	elsewhere := t.TempDir()
+	if err := os.WriteFile(filepath.Join(elsewhere, "notifier.conf"), []byte("volume = 3\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	aTemplatedModule(t, filepath.Join(tree, "modules", "notifier"), templatedNotifier, nil)
+	if err := os.Symlink(elsewhere, filepath.Join(tree, "modules", "notifier", "files")); err != nil {
+		t.Fatal(err)
+	}
+	v = gateJudged(t, f, tree, notifierTemplate)
+	if v.Verdict != "fail" || !strings.Contains(v.Report(), "files/ is a symlink") {
+		t.Fatalf("a symlinked files/ passed the gate:\n%s", v.Report())
+	}
+
+	// And the template removed from the tree fails, naming it.
+	v = gateJudged(t, f, aTemplatedTree(t, manifests, "", false), notifierTemplate)
+	if v.Verdict != "fail" || !strings.Contains(v.Report(), "files/notifier.conf") {
+		t.Fatalf("a missing template passed the gate:\n%s", v.Report())
+	}
+}
+
+// What the gate composes for the module in its template form is what the mesh composes for it inline.
+func TestTheMergeGateResolvesATemplatedModuleToItsInlineTwin(t *testing.T) {
+	dir := t.TempDir()
+	path := aTemplatedModule(t, dir, templatedNotifier, map[string]string{"files/notifier.conf": "volume = 3\n"})
+	raw, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	m, err := catalogue.ParseManifest(raw)
+	if err != nil {
+		t.Fatal(err)
+	}
+	m, err = catalogue.WithTemplatesFrom(m, dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	resolved, err := standInBuild(m)
+	if err != nil {
+		t.Fatal(err)
+	}
+	inline, err := catalogue.ParseManifest([]byte(inlineNotifier))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if builtAlike(resolved) != builtAlike(inline) {
+		got, _ := json.Marshal(resolved)
+		t.Fatalf("the templated module resolves to %s, not its inline twin", got)
+	}
+}

cmd/mesh-controller/testdata/placement-moved/anchor.json

@@ -0,0 +1,46 @@
+[
+  {
+    "id": "found.server",
+    "image": "registry.invalid:5000/library@sha256:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
+    "networks": [
+      "predecessor_default"
+    ],
+    "type": "container"
+  },
+  {
+    "id": "library.access-storage/downloads",
+    "mode": "read",
+    "path": "/storage/downloads",
+    "type": "access"
+  },
+  {
+    "id": "library.access-storage/media/series",
+    "mode": "read",
+    "path": "/storage/media/series",
+    "type": "access"
+  },
+  {
+    "id": "library.config",
+    "mode": "0750",
+    "owner": "1001:2000",
+    "path": "/var/lib/library/config",
+    "type": "directory"
+  },
+  {
+    "content": "{\n  \"accesses\": {\n    \"downloads\": \"/storage/downloads\",\n    \"series\": \"/storage/media/series\"\n  },\n  \"log\": \"warn\",\n  \"places\": {\n    \"config\": {\n      \"owner\": \"1001:2000\",\n      \"path\": \"/var/lib/library/config\"\n    }\n  },\n  \"workers\": 4\n}\n",
+    "id": "library.runtime-config",
+    "mode": "0640",
+    "path": "/var/lib/library/config/runtime.json",
+    "type": "file"
+  },
+  {
+    "id": "library.server",
+    "image": "registry.invalid:5000/library@sha256:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
+    "type": "container",
+    "volumes": [
+      "/var/lib/library/config:/config",
+      "/storage/media/series:/series",
+      "/storage/downloads:/downloads:ro"
+    ]
+  }
+]

cmd/mesh-controller/testdata/placement-moved/laptop.json

@@ -0,0 +1,37 @@
+[
+  {
+    "id": "library.access-home/media/series",
+    "mode": "read",
+    "path": "/home/media/series",
+    "type": "access"
+  },
+  {
+    "id": "library.access-storage/downloads",
+    "mode": "read",
+    "path": "/storage/downloads",
+    "type": "access"
+  },
+  {
+    "id": "library.config",
+    "mode": "0750",
+    "path": "/var/lib/library/config",
+    "type": "directory"
+  },
+  {
+    "content": "{\n  \"accesses\": {\n    \"downloads\": \"/storage/downloads\",\n    \"series\": \"/home/media/series\"\n  },\n  \"log\": \"warn\"\n}\n",
+    "id": "library.runtime-config",
+    "mode": "0640",
+    "path": "/var/lib/library/config/runtime.json",
+    "type": "file"
+  },
+  {
+    "id": "library.server",
+    "image": "registry.invalid:5000/library@sha256:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
+    "type": "container",
+    "volumes": [
+      "/var/lib/library/config:/config",
+      "/home/media/series:/series",
+      "/storage/downloads:/downloads:ro"
+    ]
+  }
+]

cmd/mesh-controller/try.go

@@ -0,0 +1,353 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"flag"
+	"fmt"
+	"net/url"
+	"os"
+	"regexp"
+	"strings"
+	"time"
+
+	"github.com/nats-io/nats.go"
+
+	"github.com/novox/mesh-controller/internal/broker"
+	"github.com/novox/mesh-controller/internal/link"
+)
+
+// A branch is tried before its pull request (novox/hq issue 686).
+//
+// A repository's store tests skip without a store, and no agent may start a database on its machine. So a
+// builder pushed, a reviewer read, and only the pull request's merge check ran those tests for the first time:
+// each failure there cost a round of fifteen to thirty minutes (mesh-controller #283, #310, #312).
+//
+// `try <owner>/<repository> <ref>` asks the build seat for the repository's own check of a pushed branch or
+// commit, as the merge check runs it (internal/builder/check.go): the ref merged into the trunk's head, the
+// trunk's merge-check.sh, each part in its toolchain's container, against a throwaway store and bus. It is a
+// check and nothing more:
+//
+//   - **no pull request, so no status**: its outcome is never said as `checked`, which is what the forge's
+//     holder sets statuses from (isTry, in Built);
+//   - **nothing registered, nothing built**: it names no module of the graph, so the merge gate does not run and
+//     no build is made for a merge (novox/hq ADR 0350's scratch builds are a pull request's check's alone);
+//   - **a check in the build queue**: after deliveries (link.KindOf, novox/hq issue 558), and bounded by the
+//     check's own bound (checkTimeout);
+//   - **the code a pull request's check would run anyway**: only a repository of the mesh, whose every pull
+//     request the build seat already checks, in containers that hold no runtime socket.
+//
+// A check outlasts a seat verb's one answer, so the ask answers its id at once and `try --id <id>` reads what
+// came of it from the build's log, where the build seat says it whole (link.StepTried): holding its answer up
+// to tryWait for a verdict, like `plans wait` (novox/hq issue 229). Nothing is kept beside the log.
+
+// tryWait is how long reading a try holds its answer for the verdict. A variable so a test need not wait.
+var tryWait = 20 * time.Second
+
+// A ref as the forge is asked for it — a branch or a commit, never an option — and a `go test -run` pattern.
+var (
+	tryRef   = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9._/-]*$`)
+	tryTests = regexp.MustCompile(`^[A-Za-z0-9_^$|().*+?/\[\]-]+$`)
+)
+
+// tryAnswer is what `try` answers, asking or reading.
+type tryAnswer struct {
+	ID string `json:"id"`
+	// State is asked (just now), waiting (nothing said of it yet: in the build queue), running, or the verdict:
+	// pass, warning (the repository declares no merge-check.sh), fail, or error (it could not run).
+	State      string   `json:"state"`
+	Said       string   `json:"said"`
+	Repository string   `json:"repository,omitempty"`
+	Ref        string   `json:"ref,omitempty"`
+	Commit     string   `json:"commit,omitempty"`
+	Base       string   `json:"base,omitempty"`
+	Trunk      string   `json:"trunk,omitempty"`
+	On         string   `json:"on,omitempty"`
+	Took       string   `json:"took,omitempty"`
+	Failed     []string `json:"failed,omitempty"`
+	// Last is the last thing the build seat said of one still running.
+	Last string `json:"last,omitempty"`
+}
+
+// isTry says a check's outcome is a try's: marked so, or — echoed by a build seat from before the mark — a
+// check of no pull request and no group, which is nobody's status either.
+func isTry(result link.BuildResult) bool {
+	c := result.Checked
+	return c != nil && (c.Try || (c.Number == 0 && c.Group == ""))
+}
+
+// asATry makes a check's ask a try's: the repository's own script alone, for no pull request.
+func asATry(request link.BuildRequest, tests string, storeOnly bool) link.BuildRequest {
+	c := *request.Check
+	c.Number, c.Try, c.Tests, c.StoreOnly = 0, true, tests, storeOnly
+	c.Paths, c.Modules, c.New, c.Dependents, c.Manifests, c.Builds = nil, nil, nil, nil, nil, nil
+	c.Judge, c.Plan, c.Group, c.Members = "", nil, "", nil
+	request.Check = &c
+	return request
+}
+
+// maxTries is how many tries may wait or run at once, mesh-wide: each holds a build machine for minutes.
+const maxTries = 4
+
+// triesIn reads the build queue for a new try of one commit: the id of a try of that commit already waiting or
+// running — the answer to a second ask — and whether there is room for another.
+func triesIn(q link.Queue, owner, repo, commit string) (same string, room bool) {
+	n := 0
+	for _, a := range q.Asks {
+		if !link.IsTry(a.Request) || (a.State != link.AskWaiting && a.State != link.AskInFlight) {
+			continue
+		}
+		n++
+		c := a.Request.Check
+		if same == "" && strings.EqualFold(c.Owner, owner) && strings.EqualFold(c.Repo, repo) && a.Request.Ref == commit {
+			same = a.ID
+		}
+	}
+	return same, n < maxTries
+}
+
+// forgeCommit asks the forge, through its module's tools on the bus, which commit a branch or commit of a
+// repository is, and the repository's default branch. A variable so a test needs no forge.
+var forgeCommit = func(ctx context.Context, owner, repo, ref string) (commit, trunk string, err error) {
+	js, err := aBus()
+	if err != nil {
+		return "", "", err
+	}
+	defer js.Close()
+	bus := link.OverNATS{Conn: js.Conn()}
+	ask := func(path string, into any) error {
+		raw, _ := json.Marshal(map[string]any{"path": path})
+		answer, err := link.Ask(ctx, bus, "gitea", "gitea_api", raw, 30*time.Second)
+		if err != nil {
+			return err
+		}
+		if answer.Error != "" {
+			return errors.New(answer.Error)
+		}
+		return json.Unmarshal(answer.Result, into)
+	}
+	var commits struct {
+		Result []struct {
+			SHA string `json:"sha"`
+		} `json:"result"`
+	}
+	if err := ask("/repos/"+owner+"/"+repo+"/commits?limit=1&stat=false&verification=false&files=false&sha="+
+		url.QueryEscape(ref), &commits); err != nil {
+		return "", "", err
+	}
+	if len(commits.Result) == 0 || commits.Result[0].SHA == "" {
+		return "", "", errors.New("the forge named no commit for it")
+	}
+	var found struct {
+		Result struct {
+			DefaultBranch string `json:"default_branch"`
+		} `json:"result"`
+	}
+	if err := ask("/repos/"+owner+"/"+repo, &found); err != nil {
+		return "", "", err
+	}
+	return commits.Result[0].SHA, found.Result.DefaultBranch, nil
+}
+
+// tryCommand is `try <owner>/<repository> <ref> [--base <branch>] [--tests <pattern>] [--store-only]`, and
+// `try --id <id>` to read what came of one.
+func tryCommand(ctx context.Context, args []string) error {
+	set := flag.NewFlagSet("try", flag.ContinueOnError)
+	base := set.String("base", "", "the branch it is merged into (the repository's default branch when none)")
+	tests := set.String("tests", "", "only the tests this `go test -run` pattern names")
+	storeOnly := set.Bool("store-only", false, "only the repository's store tests")
+	id := set.String("id", "", "a try's id: what came of it")
+	positionals, err := parseAround(set, args)
+	if err != nil {
+		return err
+	}
+	usage := errors.New("try <owner>/<repository> <branch or commit> [--base <branch>] [--tests <pattern>] " +
+		"[--store-only], or try --id <id>")
+	if *id != "" {
+		if len(positionals) != 0 {
+			return usage
+		}
+		// Before it is a token of a bus subject: an id, never a pattern.
+		if !link.SafeBuildID(*id) {
+			return fmt.Errorf("%q is not a try's id", *id)
+		}
+		return tryRead(ctx, *id)
+	}
+	if len(positionals) != 2 {
+		return usage
+	}
+	owner, repo, isPath := strings.Cut(positionals[0], "/")
+	ref := positionals[1]
+	switch {
+	case !isPath || !tryRef.MatchString(owner) || !tryRef.MatchString(repo) || strings.Contains(repo, "/"):
+		return fmt.Errorf("%q is not a repository on the forge, owner/name; nothing was asked", positionals[0])
+	case !tryRef.MatchString(ref):
+		return fmt.Errorf("%q is not a branch or a commit; nothing was asked", ref)
+	case *base != "" && !tryRef.MatchString(*base):
+		return fmt.Errorf("%q is not a branch; nothing was asked", *base)
+	case *tests != "" && !tryTests.MatchString(*tests):
+		return fmt.Errorf("%q is not a `go test -run` pattern of test names; nothing was asked", *tests)
+	}
+	// **An unknown ref is refused here, loudly** — not sent to a machine to fail at its clone minutes later.
+	commit, trunk, err := forgeCommit(ctx, owner, repo, ref)
+	if err != nil {
+		return fmt.Errorf("the forge holds no branch or commit %s in %s/%s — is it pushed? — so nothing was asked: %w",
+			ref, owner, repo, err)
+	}
+	if *base != "" {
+		trunk = *base
+	}
+	if trunk == "" {
+		return fmt.Errorf("the forge named no default branch for %s/%s, and no --base says what %s is merged into; "+
+			"nothing was asked", owner, repo, ref)
+	}
+
+	open, err := openStores(ctx)
+	if err != nil {
+		return err
+	}
+	defer open.Close()
+	entries, read, edges, err := theGraph(ctx, open.inventory)
+	if err != nil {
+		return err
+	}
+	p := link.PullUpdated{Owner: owner, Repo: repo, Base: trunk, Commit: commit}
+	// Whose repository it is, as a pull request's check reckons it: only the mesh's is tried, the code the
+	// build seat runs for every pull request already.
+	mesh := pullScope(p, entries, read, edges)
+	if !mesh.Mesh {
+		return fmt.Errorf("%s/%s is no repository of the mesh — no module is built from it and its owner is not "+
+			"the core's — and only the mesh's are tried on the build seat; nothing was asked", owner, repo)
+	}
+	request, err := checkRequestFor(ctx, open, p, checkScope{Mesh: true, From: mesh.From}, entries)
+	if err != nil {
+		return err
+	}
+	request = asATry(request, *tests, *storeOnly)
+	seat := buildSeatHeld(ctx)
+	// **Bounded in number** (novox/hq issue 686): one try of a commit at a time, and maxTries in all.
+	js, err := dialTheBus()
+	if err != nil {
+		return err
+	}
+	queue, err := link.ReadQueue(ctx, js, seat)
+	js.Close()
+	if err != nil {
+		return err
+	}
+	same, room := triesIn(queue, owner, repo, commit)
+	if same != "" {
+		return printTry(tryAnswer{ID: same, State: "asked", Repository: owner + "/" + repo, Ref: ref, Commit: commit,
+			On: seat, Said: fmt.Sprintf("a try of %s/%s at %.12s already waits or runs, as %s: nothing new was asked. "+
+				"Read it with try id=%s", owner, repo, commit, same, same)})
+	}
+	if !room {
+		return fmt.Errorf("%d tries already wait or run on the build seat, the most at once (`queue` lists them); "+
+			"nothing was asked — read one of yours, or ask again when one has ended", maxTries)
+	}
+	ask, err := askOverOn(seat)
+	if err != nil {
+		return err
+	}
+	defer ask.Close()
+	if err := ask.Ask(ctx, request); err != nil {
+		return err
+	}
+	return printTry(tryAnswer{ID: request.ID, State: "asked", Repository: owner + "/" + repo, Ref: ref, Commit: commit,
+		Base: trunk, On: seat, Said: fmt.Sprintf("asked %s to try %s/%s at %.12s (%s) merged into %s: its own "+
+			"merge-check.sh, as a check in the build queue, bounded at %s; no status is set and nothing is registered. "+
+			"Read it with try id=%s — a full run of this kind takes minutes", seat, owner, repo, commit, ref, trunk,
+			checkTimeout, request.ID)})
+}
+
+// tryRead answers what came of a try, holding the answer up to tryWait for its verdict.
+func tryRead(ctx context.Context, id string) error {
+	until := time.Now().Add(tryWait)
+	for {
+		lines, err := buildLines(ctx, id)
+		if err != nil {
+			return err
+		}
+		a := tryAnswerOf(id, lines)
+		if (a.State != "waiting" && a.State != "running") || !time.Now().Add(2*time.Second).Before(until) {
+			return printTry(a)
+		}
+		if err := sleepOrDone(ctx, 2*time.Second); err != nil {
+			return err
+		}
+	}
+}
+
+// tryAnswerOf reads a try's answer from what the build seat said of it: its outcome under StepTried; `failed`
+// for one that could not run — an error, never a pass; else how far it is.
+func tryAnswerOf(id string, lines []link.BuildLine) tryAnswer {
+	a := tryAnswer{ID: id, State: "waiting", Said: "nothing is said of " + id + " yet: it waits in the build queue " +
+		"(`queue` says where), or no try has that id; ask again"}
+	for _, l := range lines {
+		switch l.Step {
+		case link.StepTried:
+			var t link.Tried
+			if err := json.Unmarshal([]byte(l.Message), &t); err != nil || t.Verdict == "" {
+				return tryAnswer{ID: id, State: "error", Said: "the build seat's word on it cannot be read: " + l.Message}
+			}
+			return tryAnswer{ID: id, State: t.Verdict, Said: t.Summary, Took: t.Took, Commit: t.Head, Trunk: t.Trunk,
+				Failed: t.Failed}
+		case "failed":
+			return tryAnswer{ID: id, State: "error", Said: "it could not run: " + l.Message}
+		case "checked":
+			// A check that is no try, or a build seat from before the verb: its verdict is not a try's.
+			return tryAnswer{ID: id, State: "error", Said: "the build seat checked it and said no try's outcome — " +
+				"it predates the verb (novox/hq issue 686), or " + id + " is no try: " + l.Message + "; `builds` with " +
+				"the id says every line"}
+		}
+		a.State, a.Last = "running", l.Message
+		a.Said = "still running; ask again. `builds` with the id says every line so far"
+	}
+	return a
+}
+
+func printTry(a tryAnswer) error {
+	fmt.Fprintln(os.Stderr, a.Said)
+	for _, l := range a.Failed {
+		fmt.Fprintln(os.Stderr, "    "+l)
+	}
+	out, err := json.MarshalIndent(a, "", "  ")
+	if err != nil {
+		return err
+	}
+	fmt.Println(string(out))
+	return nil
+}
+
+// buildLines is everything the build seat said of one build, as the bus keeps it, in order.
+func buildLines(ctx context.Context, id string) ([]link.BuildLine, error) {
+	js, err := aBus()
+	if err != nil {
+		return nil, fmt.Errorf("cannot reach the bus to read a build's log: %w", err)
+	}
+	defer js.Close()
+	subject := link.BuildLogOf("*", id)
+	sub, err := js.Context().PullSubscribe(subject, "",
+		nats.BindStream(broker.EventsStream), nats.DeliverAll(), nats.AckNone())
+	if err != nil {
+		return nil, fmt.Errorf("cannot read %s from the bus: %w", subject, err)
+	}
+	defer func() { _ = sub.Unsubscribe() }()
+	var lines []link.BuildLine
+	for {
+		batch, err := sub.Fetch(200, nats.MaxWait(2*time.Second))
+		if err != nil && !errors.Is(err, nats.ErrTimeout) && !errors.Is(err, context.DeadlineExceeded) {
+			return nil, fmt.Errorf("reading a build's log: %w", err)
+		}
+		for _, msg := range batch {
+			var line link.BuildLine
+			if json.Unmarshal(msg.Data, &line) == nil {
+				lines = append(lines, line)
+			}
+		}
+		if len(batch) < 200 {
+			return lines, nil
+		}
+	}
+}