the unplaceable word rides a typed error, not the message (V-634)

Recovering it by cutting on quotes in err.Error() meant the reply depended on
the wording of an error string. UnknownTargetError carries the word and
errors.Is still holds.

internal/tool/tool.go

@@ -84,6 +84,17 @@ var (
 	ErrUnknownTarget = errors.New("the act names a target the system cannot have")
 )
 
+// UnknownTargetError carries the word the executor could not place, because the
+// reply names it: "«роутер» — не знаю такой цели" is actionable and "не
+// получилось" sends him to the log. errors.Is(err, ErrUnknownTarget) holds.
+type UnknownTargetError struct{ Target string }
+
+func (e *UnknownTargetError) Error() string {
+	return fmt.Sprintf("%s: %q", ErrUnknownTarget, e.Target)
+}
+
+func (e *UnknownTargetError) Unwrap() error { return ErrUnknownTarget }
+
 // MCPCaller is the seam for an act that is an MCP tool call rather than a
 // process (Vikunja #251). internal/mcp.Manager satisfies it via CallPositional.
 // nil ⇒ MCP is not configured, and an MCP row refuses to run rather than
@@ -160,7 +171,7 @@ func (e *Executor) Exec(ctx context.Context, name string, args []string, confirm
 	// since a task title is not a target, and a house row drops the spoken args.
 	if !isMCPRow(t.Cmd) && !isHouseRow(t.Cmd) {
 		if bad, ok := firstUnknownTarget(args); !ok {
-			return "", fmt.Errorf("%w: %q", ErrUnknownTarget, bad)
+			return "", &UnknownTargetError{Target: bad}
 		}
 	}
 	// The tier decides, not the column (Vikunja #449). RiskOf reads the row and
@@ -290,6 +301,10 @@ func (m *Matcher) Match(utterance string) (string, []string, bool) {
 // sentence. "перезагрузи роутер" is the case: restart is a real tool and
 // "роутер" is a real word, and `systemctl restart роутер` is neither.
 //
+// Every process row this box enables takes a system identifier (systemctl,
+// docker, journalctl, df). A process row that legitimately wanted Russian text
+// would want a different dispatch, not a hole in this check.
+//
 // It deliberately does not try to guess the right target. Identity is Nexus's
 // (CLAUDE.md § "The ecosystem"), and a target Nexus resolves reaches Hexis
 // through handleHexisAct before this executor is asked.