Try a pushed branch on the build seat before its pull request (hq issue 686)

Store tests skip without a store and no agent may start one, so each failure
cost a 15-30 minute review round. The try verb asks the build seat for the
repository's merge-check.sh on the ref merged into the trunk, as a check in
the build queue, and reads its outcome from the build's log: no status on
the forge, nothing registered, nothing built for a merge.

internal/builder/check.go

@@ -103,6 +103,23 @@ type CheckSpec struct {
 	// for the walk to take. None for a group's composed check, whose members' own checks build.
 	Builds    []CheckBuildSpec
 	BuildWith *CheckBuilding
+	// Tests and StoreOnly narrow what the repository's own script runs, for a branch tried before its pull
+	// request (novox/hq issue 686): handed to the script as EnvTests and EnvStoreOnly, which it may read.
+	Tests     string
+	StoreOnly bool
+}
+
+// selection is what a check hands the repository's script to narrow what it runs (novox/hq issue 686): nothing
+// for a pull request's check, which always runs whole.
+func selection(spec CheckSpec) []string {
+	var env []string
+	if spec.Tests != "" {
+		env = append(env, EnvTests+"="+spec.Tests)
+	}
+	if spec.StoreOnly {
+		env = append(env, EnvStoreOnly+"=1")
+	}
+	return env
 }
 
 // GroupHead is one other head of a delivery group's composed check.
@@ -193,6 +210,11 @@ const (
 	// EnvGroup is a delivery group's other heads, as JSON, for the gate (novox/hq ADR 0239); empty for a
 	// pull request checked alone.
 	EnvGroup = "MESH_CHECK_GROUP"
+	// EnvTests is a `go test -run` pattern and EnvStoreOnly is 1 when a branch tried before its pull request
+	// asks for only those tests, or only the store tests (novox/hq issue 686). Never set for a pull request's
+	// check. A script that reads neither runs whole.
+	EnvTests     = "MESH_CHECK_TESTS"
+	EnvStoreOnly = "MESH_CHECK_STORE_ONLY"
 )
 
 // CheckTimeout bounds one check; a check that runs past it is an error, not a pass.
@@ -515,6 +537,7 @@ func Check(ctx context.Context, run Runner, spec CheckSpec, workspace, registry
 		EnvModules + "=" + strings.Join(append(append([]string{}, spec.Modules...), spec.New...), ","),
 		EnvGroup + "=" + groupFile,
 		"GOCACHE=" + filepath.Join(workspace, "go-cache"), "GOMODCACHE=" + filepath.Join(workspace, "go-modules")}
+	env = append(env, selection(spec)...)
 
 	v := CheckVerdict{}
 	modules := append(append([]string{}, spec.Modules...), prefixed("new:", spec.New)...)

internal/catalogue/verbs.go

@@ -362,6 +362,25 @@ var ControllerVerbs = []Verb{
 			"register": "\"true\" to register what it builds",
 			"older":    "\"true\", with register: even though a newer build of the module is registered",
 		}, []string{"id"}, "register", "older")},
+	// novox/hq issue 686: a builder ran a branch's store tests for the first time in its pull request's merge check.
+	{Name: "try", Description: "Try a pushed branch or commit before its pull request (novox/hq issue 686): the build " +
+		"seat merges it into the repository's trunk and runs the repository's own merge-check.sh on the merge, in the " +
+		"toolchain containers and against the throwaway store and bus a pull request's merge check gets. Answers at " +
+		"once with an id; asked again with that id it waits up to 20 s and answers pass, fail or error, how long it " +
+		"took and the lines naming what failed — or that it is still waiting or running, to ask again. Sets no " +
+		"status on the forge, registers and builds nothing, runs no merge gate, counts as a check in the build queue " +
+		"(after deliveries) and is bounded as one. Only for a repository of the mesh; the ref must be on the forge.",
+		Input: schema(map[string]string{
+			"repository": "the repository on the forge, owner/name; with ref",
+			"ref":        "the branch or commit to try, as pushed to the forge",
+			"base":       "the branch it is merged into (the repository's default branch when none is named)",
+			"tests": "only the tests this `go test -run` pattern names, where the repository's merge-check.sh reads " +
+				"MESH_CHECK_TESTS; a script that does not runs whole",
+			"store-only": "\"true\": only the repository's store tests, where its merge-check.sh reads " +
+				"MESH_CHECK_STORE_ONLY",
+			"id": "instead of a repository: the id a try answered, to read what came of it",
+		}, nil, "store-only"),
+		Replaces: []string{"sh merge-check.sh", "docker run postgres"}},
 	// novox/hq ADR 0350 §5: asked by the delivery's owner when the forge says a pull request closed unmerged.
 	{Name: "forget-checks", Description: "Let go of every build a pull request's merge checks made for its merge in " +
 		"the artifact store's scratch namespace (novox/hq ADR 0350 §5): asked when it closed unmerged; a merged one's go " +

internal/link/build.go

@@ -164,6 +164,30 @@ type CheckRequest struct {
 	// each, from the merge it judged, into the scratch namespace once it has judged and not failed, for the walk to
 	// take. A build seat from before it builds nothing, and the walk builds as before.
 	Builds []CheckBuild `json:"builds,omitempty"`
+	// Try marks a branch tried before its pull request (novox/hq issue 686): the repository's own check for a
+	// pushed branch or commit, asked by a builder through the controller's `try` verb. Its outcome is read from
+	// the build's log (StepTried) and said to nobody: no status on the forge, nothing recorded or registered,
+	// nothing built for a merge. Tests narrows what the repository's script runs to the tests a pattern names,
+	// and StoreOnly to its store tests; a script that reads neither runs whole.
+	Try       bool   `json:"try,omitempty"`
+	Tests     string `json:"tests,omitempty"`
+	StoreOnly bool   `json:"store-only,omitempty"`
+}
+
+// StepTried is the step a build seat says a try's outcome under, in the build's log: one line, a Tried as JSON
+// (novox/hq issue 686).
+const StepTried = "tried"
+
+// Tried is what came of a branch tried before its pull request (novox/hq issue 686): the verdict of the
+// repository's own check for the ref merged into the trunk, how long it took, and the lines that name what
+// failed, picked from the whole of its output (issue 460).
+type Tried struct {
+	Verdict string   `json:"verdict"`
+	Summary string   `json:"summary"`
+	Took    string   `json:"took"`
+	Head    string   `json:"head,omitempty"`
+	Trunk   string   `json:"trunk,omitempty"`
+	Failed  []string `json:"failed,omitempty"`
 }
 
 // CheckBuild is one module a check builds for its merge: from the merge it made when Merged — a module built from