GATE7 (source part, §690): the gate's source answers a branch's source key, or the branches it keeps

The gate's source value is the contract's SourceByBranchValue and its key SourceKey(branch); the verb takes an optional
branch and answers branches alone when given none. The whole-module package does not compile on the join for GATE11
(settle) and GATE17 (ledger fill and remove), so the unit suite was run with those five sites stubbed in a scratch edit,
never committed: green apart from the stubbed removal case.

Builds: design 47 G §690, §614, §15

Claude-Session: https://claude.ai/code/session_01JG73KEq4zoDfM9WtYpcQgZ

modules/mesh-delivery-gate/cmd/mesh-delivery-gate/bridge_test.go

@@ -178,17 +178,27 @@ func (s *fakeSource) Move(update func(prev *Source) (Source, bool)) error {
 	return nil
 }
 
-// Read is source.main as held, and its revision: the number of writes.
-func (s *fakeSource) Read() (*Source, uint64, error) {
+// Read is a branch's source key as held, and its revision: the number of writes. The fake holds the key of MergeBranch only.
+func (s *fakeSource) Read(branch string) (*Source, uint64, error) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
-	if s.main == nil {
+	if s.main == nil || branch != MergeBranch {
 		return nil, 0, nil
 	}
 	held := *s.main
 	return &held, uint64(len(s.moves)), nil
 }
 
+// Branches are the branches whose source key the fake holds.
+func (s *fakeSource) Branches() ([]string, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if s.main == nil {
+		return nil, nil
+	}
+	return []string{MergeBranch}, nil
+}
+
 func sortStrings(s []string) { sort.Strings(s) }
 func itoa(n int) string      { return strconv.Itoa(n) }
 

modules/mesh-delivery-gate/cmd/mesh-delivery-gate/bus_test.go

@@ -639,7 +639,7 @@ func TestAPassingVerdictAsksTheApproveAndItsApproveMergesWithinSecondsOverARealB
 	// The forge's own word that the pull request merged follows the bridge's (its webhook): the delivery ends merged.
 	b.publish(t, "mesh.seat.git.event.pull.merged", seatMerged(merged("novox/app", 7, head, strings.Repeat("b", 40))))
 	rt.until("source.main to hold the merge", eventWithin, func() bool {
-		e, err := b.kvs["source"].Get(ctx, mdc.SourceMainKey)
+		e, err := b.kvs["source"].Get(ctx, mdc.SourceKey(MergeBranch))
 		if err != nil {
 			return false
 		}
@@ -864,7 +864,7 @@ func TestAGroupOfTwoWithGreenChecksGetsOneAskAndOnItsApproveBothMergeOneAfterThe
 	b.forgeSays(t, forgemsg.Forge{Kind: forgemsg.ForgeMerged, Repository: two.Repository, Number: two.Number, Head: two.Head.Head,
 		Merge: strings.Repeat("b", 40), Root: "r", Trees: map[string]string{"x": "t"}})
 	rt.until("source.main to hold both merges", eventWithin, func() bool {
-		e, err := b.kvs["source"].Get(ctx, mdc.SourceMainKey)
+		e, err := b.kvs["source"].Get(ctx, mdc.SourceKey(MergeBranch))
 		if err != nil {
 			return false
 		}

modules/mesh-delivery-gate/cmd/mesh-delivery-gate/issue888_test.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"reflect"
 	"testing"
 	"time"
 
@@ -41,11 +42,18 @@ func TestAMergeHeardOnlyFromTheForgeMovesSourceMain(t *testing.T) {
 		t.Fatalf("source.main is %+v; wanted %s at %s and %s kept", w.source.main, i888App, i888Merge1, i888Other)
 	}
 	// The seat's verb source answers each repository's trunk branch and head, and the revision, from the same key.
-	if a := w.h.SourceRevision(); a.Error != "" || a.Revision != 1 || len(a.Repositories) != 2 ||
+	if a := w.h.SourceRevision(MergeBranch); a.Error != "" || a.Revision != 1 || len(a.Repositories) != 2 ||
 		a.Repositories[0] != (seat.SourceHead{Repository: i888App, Trunk: MergeBranch, Head: i888Merge1}) ||
 		a.Repositories[1].Repository != i888Other || a.Repositories[1].Head != i888OtherH {
 		t.Fatalf("source answers %+v", a)
 	}
+	// §690: given no branch it answers the branches of the keys it keeps, and no repository; a branch it keeps no key of has none.
+	if a := w.h.SourceRevision(""); a.Error != "" || !reflect.DeepEqual(a.Branches, []string{MergeBranch}) || len(a.Repositories) != 0 || a.Revision != 0 {
+		t.Fatalf("source with no branch answers %+v, want the branches %v alone", a, []string{MergeBranch})
+	}
+	if a := w.h.SourceRevision("beta"); a.Error != "" || a.Branch != "beta" || a.Revision != 0 || len(a.Repositories) != 0 {
+		t.Fatalf("source of a branch with no key answers %+v", a)
+	}
 	n := len(w.source.moves)
 	w.settleAll()
 	w.h.PullMerged(i888MergedAt(i888App, 3, i888Head1, i888Merge1, w.now.Add(-time.Minute))) // heard again

modules/mesh-delivery-gate/cmd/mesh-delivery-gate/main.go

@@ -345,8 +345,9 @@ func tools(h *Holder, l *listening) []stdio.Tool {
 			Description: "The source revision the gate holds: every repository it names, its trunk branch and that trunk's head, the " +
 				"group that moved it last and its revision. Read, never written: a node-engine reads the repositories here to call a " +
 				"reverted build's catch-up tool once per repository, never the gate's state.",
-			Input: map[string]any{"type": "object", "properties": map[string]any{}},
-			Run:   func(map[string]any) (any, error) { return h.SourceRevision(), nil }},
+			Input: map[string]any{"type": "object", "properties": map[string]any{
+				"branch": str("the watched branch, escaped as a key name is; absent: the list of the branches the gate keeps a source revision of")}},
+			Run: func(a map[string]any) (any, error) { return h.SourceRevision(strArg(a, "branch")), nil }},
 		{Name: seat + "checks",
 			Description: "What the mesh's checks said of a pull request's head or of one commit: each of the commit's " +
 				"statuses (mesh/check, mesh/delivery, …) with its state, description and when it " +

modules/mesh-delivery-gate/cmd/mesh-delivery-gate/merges.go

@@ -14,6 +14,7 @@ import (
 	seat "git.novox.be/novox/mesh-delivery/contracts/go/seats/meshdelivery"
 	"git.novox.be/novox/mesh-delivery/modules/mesh-delivery-forge-bridge/forgemsg"
 	stdio "git.novox.be/novox/mesh-sdk/go"
+	"git.novox.be/novox/mesh-sdk/go/keys"
 )
 
 // The gate merges through the forge bridge, never itself (novox/hq ADR 0437 §8, ADR 0441 §5, ADR 0450 §3). It writes into
@@ -48,13 +49,15 @@ func (kvOld) Get(state, key string) ([]byte, uint64, error) {
 	return e.Value, e.Revision, nil
 }
 
-// SourceStore is the gate's bucket source, one key, moved by compare-and-set.
+// SourceStore is the gate's bucket source, one key per watched branch (design 47 G §15), moved by compare-and-set.
 type SourceStore interface {
-	// Move reads source.main and writes what update makes of it, unless update says nothing is to be written; a write
-	// another writer won is read again and tried again.
+	// Move reads the source key of the gate's merge branch (MergeBranch) and writes what update makes of it, unless update
+	// says nothing is to be written; a write another writer won is read again and tried again.
 	Move(update func(prev *Source) (Source, bool)) error
-	// Read is source.main as held and its revision on the bus; nil and 0 before it is first written.
-	Read() (*Source, uint64, error)
+	// Read is a branch's source key as held and its revision on the bus; nil and 0 before it is first written.
+	Read(branch string) (*Source, uint64, error)
+	// Branches are the branch names of the source keys the gate keeps (§614, §690).
+	Branches() ([]string, error)
 }
 
 // kvMerges is merges over the runtime.
@@ -95,7 +98,7 @@ type kvSource struct{}
 func (kvSource) Move(update func(prev *Source) (Source, bool)) error {
 	state := stdio.State("source")
 	for range changeAttempts {
-		e, err := state.Get(mdc.SourceMainKey)
+		e, err := state.Get(mdc.SourceKey(MergeBranch))
 		if err != nil {
 			return err
 		}
@@ -116,9 +119,9 @@ func (kvSource) Move(update func(prev *Source) (Source, bool)) error {
 			return err
 		}
 		if e == nil {
-			_, err = state.Create(mdc.SourceMainKey, json.RawMessage(raw))
+			_, err = state.Create(mdc.SourceKey(MergeBranch), json.RawMessage(raw))
 		} else {
-			_, err = state.Update(mdc.SourceMainKey, json.RawMessage(raw), e.Revision)
+			_, err = state.Update(mdc.SourceKey(MergeBranch), json.RawMessage(raw), e.Revision)
 		}
 		if err == nil {
 			return nil
@@ -130,33 +133,64 @@ func (kvSource) Move(update func(prev *Source) (Source, bool)) error {
 	return fmt.Errorf("source.main was written by another writer first %d times: %w", changeAttempts, stdio.ErrChanged)
 }
 
-func (kvSource) Read() (*Source, uint64, error) {
-	e, err := stdio.State("source").Get(mdc.SourceMainKey)
+func (kvSource) Read(branch string) (*Source, uint64, error) {
+	e, err := stdio.State("source").Get(mdc.SourceKey(branch))
 	if err != nil || e == nil {
 		return nil, 0, err
 	}
 	held, err := mdc.DecodeSource(e.Value)
 	if err != nil {
-		return nil, 0, fmt.Errorf("source.main is not readable: %w", err)
+		return nil, 0, fmt.Errorf("source.%s is not readable: %w", branch, err)
 	}
 	return &held, e.Revision, nil
 }
 
-// SourceRevision is the seat's verb source: every repository source.main names, its trunk branch and head, the group that
-// moved it last and its revision, or why it cannot be read. source.main names each repository's main only (MergeBranch).
-// Outside the lock.
-func (h *Holder) SourceRevision() seat.SourceAnswer {
+func (kvSource) Branches() ([]string, error) {
+	names, err := stdio.State("source").Keys()
+	if err != nil {
+		return nil, err
+	}
+	var out []string
+	for _, key := range names {
+		escaped, ok := seat.ParseSourceByBranchKey(key)
+		if !ok {
+			continue
+		}
+		branch, err := keys.UnescapeName(escaped)
+		if err != nil {
+			return nil, fmt.Errorf("the source key %q is not a branch's: %w", key, err)
+		}
+		out = append(out, branch)
+	}
+	sort.Strings(out)
+	return out, nil
+}
+
+// SourceRevision is the seat's verb source (§690): given a branch, every repository that branch's source key names, its
+// trunk branch and head, the group that moved it last and its revision, or why it cannot be read; given none, `branches`,
+// the branch of each source key the gate keeps. A key names each repository's merge branch only (MergeBranch). Outside the lock.
+func (h *Holder) SourceRevision(branch string) seat.SourceAnswer {
 	if h.Source == nil {
 		return seat.SourceAnswer{Error: "no source bucket"}
 	}
-	held, revision, err := h.Source.Read()
+	if branch == "" {
+		branches, err := h.Source.Branches()
+		if err != nil {
+			return seat.SourceAnswer{Error: err.Error()}
+		}
+		if branches == nil {
+			branches = []string{}
+		}
+		return seat.SourceAnswer{Branches: branches}
+	}
+	held, revision, err := h.Source.Read(branch)
 	if err != nil {
 		return seat.SourceAnswer{Error: err.Error()}
 	}
 	if held == nil {
-		return seat.SourceAnswer{}
+		return seat.SourceAnswer{Branch: branch}
 	}
-	out := seat.SourceAnswer{Group: held.Group, Revision: int64(revision)}
+	out := seat.SourceAnswer{Branch: branch, Group: held.Group, Revision: int64(revision)}
 	for repository, head := range held.Heads {
 		out.Repositories = append(out.Repositories, seat.SourceHead{Repository: repository, Trunk: MergeBranch, Head: head})
 	}

modules/mesh-delivery-gate/cmd/mesh-delivery-gate/values.go

@@ -22,7 +22,7 @@ const (
 // are converted at the edge, so a stored value decodes unchanged (novox/hq ADR 0634 §2).
 type (
 	// Source is the state source's value.
-	Source = seat.SourceByMainValue
+	Source = seat.SourceByBranchValue
 	// Owed is the state owed's value: what the forge bridge performs.
 	Owed = seat.OwedByRepositoryNumberHeadActValue
 	// Answer is the operator's answer as the gate acts on it.