node-tools: a tool call names its caller, and the module is told it from the subject (hq issue 365)

Each tool and seat verb is also served on its caller-named subject, kind call
with the caller's bus user last, which the controller grants each user with its
own name alone; the runtime hands the module that caller in the call's _meta,
never from the body. Calls through the runtime (the console and modules'
invokes) ask the caller-named subject first and the old one only when the first
reached nobody: nothing serves it yet, or the bus refused it because the grant
is not delivered yet, which ends the call at once rather than after 30 s. The
old subjects stay served and say no caller for one release (hq issue 464).

node-tools/internal/launch/launch.go

@@ -37,7 +37,24 @@ type Tool struct {
 	Name        string
 	Description string
 	Input       json.RawMessage
-	Run         func(args json.RawMessage) (json.RawMessage, error)
+	// Run calls the tool for caller: the bus user the call's subject named, or "" when it named none. A
+	// caller is handed to the bundle in the call's `_meta` (MetaCaller), never among its arguments.
+	Run func(caller string, args json.RawMessage) (json.RawMessage, error)
+}
+
+// MetaCaller is where in a `tools/call`'s `_meta` the runtime names the caller it took from the subject the
+// call arrived on (novox/hq issue 365): mesh-sdk's stdio.MetaCaller, which hands it to the tool as
+// stdio.CallerOf, and says Unproven when it is absent.
+const MetaCaller = "mesh/caller"
+
+// callParams is a `tools/call`'s params: the tool, its arguments as the caller sent them, and — only when the
+// subject named one — the caller, in `_meta`, which the runtime writes and no caller can.
+func callParams(name, caller string, args json.RawMessage) map[string]any {
+	params := map[string]any{"name": name, "arguments": args}
+	if caller != "" {
+		params["_meta"] = map[string]any{MetaCaller: caller}
+	}
+	return params
 }
 
 // Registration is the tools a bundle listed under one name: its module's, or a seat's.
@@ -484,11 +501,11 @@ func Start(module, entry string, env []string, mesh Bus, logf func(string, ...an
 			input = json.RawMessage("{}")
 		}
 		tool := Tool{Name: name, Description: t.Description, Input: input,
-			Run: func(args json.RawMessage) (json.RawMessage, error) {
+			Run: func(caller string, args json.RawMessage) (json.RawMessage, error) {
 				if len(args) == 0 || string(args) == "null" {
 					args = json.RawMessage("{}")
 				}
-				res, err := asking("tools/call", map[string]any{"name": full, "arguments": args}, CallTimeout)
+				res, err := asking("tools/call", callParams(full, caller, args), CallTimeout)
 				if err != nil {
 					return nil, err
 				}