feat(slot): Add merge-slot gate for serialized conflict resolution

Adds a new slot bead type and merge-slot commands for serializing
conflict resolution in the merge queue. This prevents "monkey knife
fights" where multiple polecats race to resolve conflicts.

- Add TypeSlot to bead types
- Add Holder field to Issue struct
- Add bd merge-slot create/check/acquire/release commands
- Add Holder field to UpdateArgs in RPC protocol

(gt-4u49x)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/rpc/protocol.go

@@ -164,6 +164,8 @@ type UpdateArgs struct {
 	// Gate fields
 	AwaitID *string  `json:"await_id,omitempty"` // Condition identifier for gates (run ID, PR number, etc.)
 	Waiters []string `json:"waiters,omitempty"`  // Mail addresses to notify when gate clears
+	// Slot fields
+	Holder *string `json:"holder,omitempty"` // Who currently holds the slot (for type=slot beads)
 }
 
 // CloseArgs represents arguments for the close operation

internal/rpc/server_issues_epics.go

@@ -142,6 +142,10 @@ func updatesFromArgs(a UpdateArgs) map[string]interface{} {
 	if len(a.Waiters) > 0 {
 		u["waiters"] = a.Waiters
 	}
+	// Slot fields
+	if a.Holder != nil {
+		u["holder"] = *a.Holder
+	}
 	return u
 }
 

internal/types/types.go

@@ -91,6 +91,9 @@ type Issue struct {
 	Timeout   time.Duration `json:"timeout,omitempty"`    // Max wait time before escalation
 	Waiters   []string      `json:"waiters,omitempty"`    // Mail addresses to notify when gate clears
 
+	// ===== Slot Fields (exclusive access primitives) =====
+	Holder string `json:"holder,omitempty"` // Who currently holds the slot (empty = available)
+
 	// ===== Source Tracing Fields (formula cooking origin) =====
 	SourceFormula  string `json:"source_formula,omitempty"`  // Formula name where step was defined
 	SourceLocation string `json:"source_location,omitempty"` // Path: "steps[0]", "advice[0].after"
@@ -163,6 +166,9 @@ func (i *Issue) ComputeContentHash() string {
 		w.str(waiter)
 	}
 
+	// Slot fields for exclusive access
+	w.str(i.Holder)
+
 	// Agent identity fields
 	w.str(i.HookBead)
 	w.str(i.RoleBead)
@@ -413,12 +419,13 @@ const (
 	TypeRole         IssueType = "role"          // Agent role definition
 	TypeConvoy       IssueType = "convoy"        // Cross-project tracking with reactive completion
 	TypeEvent        IssueType = "event"         // Operational state change record
+	TypeSlot         IssueType = "slot"          // Exclusive access slot (merge-slot gate)
 )
 
 // IsValid checks if the issue type value is valid
 func (t IssueType) IsValid() bool {
 	switch t {
-	case TypeBug, TypeFeature, TypeTask, TypeEpic, TypeChore, TypeMessage, TypeMergeRequest, TypeMolecule, TypeGate, TypeAgent, TypeRole, TypeConvoy, TypeEvent:
+	case TypeBug, TypeFeature, TypeTask, TypeEpic, TypeChore, TypeMessage, TypeMergeRequest, TypeMolecule, TypeGate, TypeAgent, TypeRole, TypeConvoy, TypeEvent, TypeSlot:
 		return true
 	}
 	return false