Make the login shell's execute optional, so a machine may withhold it

execute runs any command as the operator account, which can become root
without a person. The operator withholds it on the control-node until a
call needs a person's approval (hq ADR 0268); the holder withholds it per
machine through its own setting. With execute required, that holder could
not hold the seat there and would be judged silent. ADR 0246's optional
mark lets it hold the seat without serving the verb.

cmd/mesh-controller/holders_silent_test.go

@@ -92,3 +92,26 @@ func TestHoldingNeedsAnAnswer(t *testing.T) {
 		}
 	}
 }
+
+// The control-node withholds the login shell's `execute` (novox/hq ADR 0268): its holder there serves
+// nothing on the seat, and must not be judged silent for it, as the store's rows read it back.
+func TestALoginShellWithholdingExecuteIsNotSilent(t *testing.T) {
+	defer catalogue.UseSeats(catalogue.DefaultSeats())
+	var rows []catalogue.Seat
+	for _, s := range catalogue.DefaultSeats() {
+		stored := s
+		stored.Serves = nil
+		for _, v := range s.Serves {
+			v.Optional = false // the store never keeps the mark
+			stored.Serves = append(stored.Serves, v)
+		}
+		rows = append(rows, stored)
+	}
+	catalogue.UseSeats(rows)
+	recorded := []catalogue.Held{{Claim: catalogue.LoginShellSeat, Scope: catalogue.ScopeNode, Node: "anchor", Module: "zsh"}}
+	expected := holdersToHear(catalogue.SeatsWithAProtocol(), recorded, nil, map[string]bool{"anchor": true}, nil, time.Now())
+	if _, asked := expected[catalogue.LoginShellSeat]; asked {
+		t.Fatalf("the login shell's holder is expected to answer, so withholding execute would be said silent: %v",
+			expected[catalogue.LoginShellSeat])
+	}
+}

internal/catalogue/login_shell_execute_test.go

@@ -0,0 +1,41 @@
+package catalogue
+
+import "testing"
+
+// The login shell's `execute` runs any command as the operator account, which can become root without a
+// person, so the operator withheld it on the control-node until a call to it needs a person's approval
+// (novox/hq ADR 0268). It is withheld per machine by the holder's own setting, so the seat must let a
+// holder hold it without serving the verb there: `execute` is optional (ADR 0246's mark), and stays so in
+// a seat row read back from the store, which never keeps the mark.
+func TestTheLoginShellsExecuteIsOptionalSoAMachineMayWithholdIt(t *testing.T) {
+	check := func(t *testing.T) {
+		t.Helper()
+		seat, ok := SeatNamed(LoginShellSeat)
+		if !ok {
+			t.Fatal("node-login-shell is not defined")
+		}
+		if len(seat.Serves) != 1 || seat.Serves[0].Name != "execute" {
+			t.Fatalf("the login shell promises %+v, not execute alone", seat.Serves)
+		}
+		if !seat.Serves[0].Optional {
+			t.Fatal("execute is required, so a holder that withholds it on one machine could not hold the seat there")
+		}
+		withholding := Manifest{Module: "zsh", Version: "1", Claims: []Claim{{Name: LoginShellSeat, Scope: ScopeNode}}}
+		if err := CanHold(withholding, seat); err != nil {
+			t.Fatalf("a holder serving no execute is refused: %v", err)
+		}
+		serving := withholding
+		serving.Claims = []Claim{{Name: LoginShellSeat, Scope: ScopeNode, Serves: []string{"execute"}}}
+		if err := CanHold(serving, seat); err != nil {
+			t.Fatalf("a holder serving execute is refused: %v", err)
+		}
+	}
+	t.Run("compiled", check)
+	t.Run("read back from the store", func(t *testing.T) {
+		before := seats
+		t.Cleanup(func() { seats = before })
+		UseSeats([]Seat{{Name: LoginShellSeat, Scope: ScopeNode, Decision: "novox/hq ADR 0204",
+			Serves: []Verb{{Name: "execute"}}}})
+		check(t)
+	})
+}

internal/catalogue/seats.go

@@ -256,8 +256,9 @@ var defaultSeats = append([]Seat{
 	{Name: EnvironmentSeat, Scope: ScopeNode, Decision: "novox/hq ADR 0203"},
 	// The login shell (novox/hq ADR 0204, replacing the module-declared `login-shell` of ADR 0176):
 	// the mesh's, so a second shell module claims the seat rather than declaring a second one, and
-	// the seat exists whether or not zsh's definition is registered. `execute` is the contract any
-	// node may call; the holder places every module's shell code in its slots.
+	// the seat exists whether or not zsh's definition is registered. `execute` is the contract a caller
+	// may call where the machine serves it (optional: ADR 0268); the holder places every module's shell
+	// code in its slots.
 	{Name: LoginShellSeat, Scope: ScopeNode, Decision: "novox/hq ADR 0204",
 		Serves: loginShellVerbs()},
 	// A machine's power (novox/hq ADR 0211): its holder owns logind's power handling, places the
@@ -721,9 +722,6 @@ func uplinkVerbs() []Verb {
 	}
 }
 
-// loginShellVerbs is the contract every holder of node-login-shell serves (novox/hq ADR 0176, ADR
-// 0204): one command, run the way the operator's own terminal would run it, bounded below the
-// runtime's thirty-second call limit so a hung command answers rather than times the caller out.
 // backupVerbs is the node-backup seat's protocol (novox/hq to-be 43): what is kept, take one now,
 // and restore beside the live data — never over it.
 func backupVerbs() []Verb {
@@ -745,9 +743,18 @@ func backupVerbs() []Verb {
 	}
 }
 
+// loginShellVerbs is the contract of node-login-shell (novox/hq ADR 0176, ADR 0204): one command, run
+// the way the operator's own terminal would run it, bounded below the runtime's thirty-second call limit
+// so a hung command answers rather than times the caller out.
+//
+// **`execute` is optional** (novox/hq ADR 0268). It runs any command as the operator account, which can
+// become root without a person, so a machine may withhold it: the control-node does, through the
+// holder's own `execute` setting, until a call to it needs a person's approval (hq research 039). The mark
+// is ADR 0246's: a holder that does not serve the verb on a machine still holds the seat there, and its
+// silence on the bus is not judged — a holder withholding it serves nothing on the seat.
 func loginShellVerbs() []Verb {
 	return []Verb{
-		{Name: "execute", Description: "Run one command on this machine as the operator account, in a " +
+		{Name: "execute", Optional: true, Description: "Run one command on this machine as the operator account, in a " +
 			"non-interactive login shell in its home; answers with what it printed and how it exited.",
 			Input: schema(map[string]string{
 				"command":         "the command line, as you would type it",