Bring main into release 57's branch, conflicts resolved

So the release branch carries what main gained, and the store-tests drop check passes again.

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

internal/link/builds.go

@@ -96,8 +96,27 @@ type BuildStart struct {
 	// an earlier taker left unfinished — most often a build agent replaced mid-build — and started
 	// again from the beginning (novox/hq issue 594). 0 from a machine that predates it.
 	Delivery int `json:"delivery,omitempty"`
+	// Try marks the start of a branch tried before its pull request (novox/hq issue 686), which names no
+	// repository and no ref (startOf).
+	Try bool `json:"try,omitempty"`
 }
 
+// startOf is what a build machine says of the ask it took. **A try's start names no repository and no commit**
+// (novox/hq issue 686): the forge's holder writes mesh/merge-gate pending on an open pull request whose head is
+// the commit a start names, and a try of that head is no check of the pull request — nothing on the forge moves
+// for a try. Its id, machine and time are all the queue reads of a start.
+func startOf(r BuildRequest, on string, delivery int, at time.Time) BuildStart {
+	s := BuildStart{ID: r.ID, Repository: r.Repository, Path: r.Path, Ref: r.Ref, On: on,
+		At: at.UTC().Format(time.RFC3339Nano), Delivery: delivery}
+	if IsTry(r) {
+		s.Repository, s.Path, s.Ref, s.Try = "", "", "", true
+	}
+	return s
+}
+
+// IsTry says an ask is a branch tried before its pull request (novox/hq issue 686).
+func IsTry(r BuildRequest) bool { return r.Check != nil && r.Check.Try }
+
 // Restarted is how a build handed out again says so (novox/hq issue 594), in its log and in its check's
 // report, so a second run never reads as the first. Neutral on why: a holder replaced mid-build, a paused
 // holder handing an ask back as it arrived, and a bus that held its acknowledgements past the wait all